can_rcv_msg is now a VC flag (XCC)

[akaros.git] / kern / src / process.c

/* Copyright (c) 2009, 2010 The Regents of the University of California
 * Barret Rhoden <brho@cs.berkeley.edu>
 * See LICENSE for details. */

#ifdef __SHARC__
#pragma nosharc
#endif

#include <ros/bcq.h>
#include <event.h>
#include <arch/arch.h>
#include <bitmask.h>
#include <process.h>
#include <atomic.h>
#include <smp.h>
#include <pmap.h>
#include <trap.h>
#include <schedule.h>
#include <manager.h>
#include <stdio.h>
#include <assert.h>
#include <time.h>
#include <hashtable.h>
#include <slab.h>
#include <sys/queue.h>
#include <frontend.h>
#include <monitor.h>
#include <elf.h>
#include <arsc_server.h>
#include <devfs.h>

struct kmem_cache *proc_cache;

/* Other helpers, implemented later. */
static void __proc_startcore(struct proc *p, trapframe_t *tf);
static bool is_mapped_vcore(struct proc *p, uint32_t pcoreid);
static uint32_t get_vcoreid(struct proc *p, uint32_t pcoreid);
static uint32_t try_get_pcoreid(struct proc *p, uint32_t vcoreid);
static uint32_t get_pcoreid(struct proc *p, uint32_t vcoreid);
static void __proc_free(struct kref *kref);
static bool scp_is_vcctx_ready(struct preempt_data *vcpd);

/* PID management. */
#define PID_MAX 32767 // goes from 0 to 32767, with 0 reserved
static DECL_BITMASK(pid_bmask, PID_MAX + 1);
spinlock_t pid_bmask_lock = SPINLOCK_INITIALIZER;
struct hashtable *pid_hash;
spinlock_t pid_hash_lock; // initialized in proc_init

/* Finds the next free entry (zero) entry in the pid_bitmask.  Set means busy.
 * PID 0 is reserved (in proc_init).  A return value of 0 is a failure (and
 * you'll also see a warning, for now).  Consider doing this with atomics. */
static pid_t get_free_pid(void)
{
        static pid_t next_free_pid = 1;
        pid_t my_pid = 0;

        spin_lock(&pid_bmask_lock);
        // atomically (can lock for now, then change to atomic_and_return
        FOR_CIRC_BUFFER(next_free_pid, PID_MAX + 1, i) {
                // always points to the next to test
                next_free_pid = (next_free_pid + 1) % (PID_MAX + 1);
                if (!GET_BITMASK_BIT(pid_bmask, i)) {
                        SET_BITMASK_BIT(pid_bmask, i);
                        my_pid = i;
                        break;
                }
        }
        spin_unlock(&pid_bmask_lock);
        if (!my_pid)
                warn("Shazbot!  Unable to find a PID!  You need to deal with this!\n");
        return my_pid;
}

/* Return a pid to the pid bitmask */
static void put_free_pid(pid_t pid)
{
        spin_lock(&pid_bmask_lock);
        CLR_BITMASK_BIT(pid_bmask, pid);
        spin_unlock(&pid_bmask_lock);
}

/* While this could be done with just an assignment, this gives us the
 * opportunity to check for bad transitions.  Might compile these out later, so
 * we shouldn't rely on them for sanity checking from userspace.  */
int __proc_set_state(struct proc *p, uint32_t state)
{
        uint32_t curstate = p->state;
        /* Valid transitions:
         * C   -> RBS
         * C   -> D
         * RBS -> RGS
         * RGS -> RBS
         * RGS -> W
         * RGM -> W
         * W   -> RBS
         * W   -> RBM
         * RGS -> RBM
         * RBM -> RGM
         * RGM -> RBM
         * RGM -> RBS
         * RGS -> D
         * RGM -> D
         *
         * These ought to be implemented later (allowed, not thought through yet).
         * RBS -> D
         * RBM -> D
         */
        #if 1 // some sort of correctness flag
        switch (curstate) {
                case PROC_CREATED:
                        if (!(state & (PROC_RUNNABLE_S | PROC_DYING)))
                                panic("Invalid State Transition! PROC_CREATED to %02x", state);
                        break;
                case PROC_RUNNABLE_S:
                        if (!(state & (PROC_RUNNING_S | PROC_DYING)))
                                panic("Invalid State Transition! PROC_RUNNABLE_S to %02x", state);
                        break;
                case PROC_RUNNING_S:
                        if (!(state & (PROC_RUNNABLE_S | PROC_RUNNABLE_M | PROC_WAITING |
                                       PROC_DYING)))
                                panic("Invalid State Transition! PROC_RUNNING_S to %02x", state);
                        break;
                case PROC_WAITING:
                        if (!(state & (PROC_RUNNABLE_S | PROC_RUNNABLE_M)))
                                panic("Invalid State Transition! PROC_WAITING to %02x", state);
                        break;
                case PROC_DYING:
                        if (state != PROC_CREATED) // when it is reused (TODO)
                                panic("Invalid State Transition! PROC_DYING to %02x", state);
                        break;
                case PROC_RUNNABLE_M:
                        if (!(state & (PROC_RUNNING_M | PROC_DYING)))
                                panic("Invalid State Transition! PROC_RUNNABLE_M to %02x", state);
                        break;
                case PROC_RUNNING_M:
                        if (!(state & (PROC_RUNNABLE_S | PROC_RUNNABLE_M | PROC_WAITING |
                                       PROC_DYING)))
                                panic("Invalid State Transition! PROC_RUNNING_M to %02x", state);
                        break;
        }
        #endif
        p->state = state;
        return 0;
}

/* Returns a pointer to the proc with the given pid, or 0 if there is none.
 * This uses get_not_zero, since it is possible the refcnt is 0, which means the
 * process is dying and we should not have the ref (and thus return 0).  We need
 * to lock to protect us from getting p, (someone else removes and frees p),
 * then get_not_zero() on p.
 * Don't push the locking into the hashtable without dealing with this. */
struct proc *pid2proc(pid_t pid)
{
        spin_lock(&pid_hash_lock);
        struct proc *p = hashtable_search(pid_hash, (void*)(long)pid);
        if (p)
                if (!kref_get_not_zero(&p->p_kref, 1))
                        p = 0;
        spin_unlock(&pid_hash_lock);
        return p;
}

/* Performs any initialization related to processes, such as create the proc
 * cache, prep the scheduler, etc.  When this returns, we should be ready to use
 * any process related function. */
void proc_init(void)
{
        /* Catch issues with the vcoremap and TAILQ_ENTRY sizes */
        static_assert(sizeof(TAILQ_ENTRY(vcore)) == sizeof(void*) * 2);
        proc_cache = kmem_cache_create("proc", sizeof(struct proc),
                     MAX(HW_CACHE_ALIGN, __alignof__(struct proc)), 0, 0, 0);
        /* Init PID mask and hash.  pid 0 is reserved. */
        SET_BITMASK_BIT(pid_bmask, 0);
        spinlock_init(&pid_hash_lock);
        spin_lock(&pid_hash_lock);
        pid_hash = create_hashtable(100, __generic_hash, __generic_eq);
        spin_unlock(&pid_hash_lock);
        schedule_init();

        atomic_init(&num_envs, 0);
}

/* Be sure you init'd the vcore lists before calling this. */
static void proc_init_procinfo(struct proc* p)
{
        p->procinfo->pid = p->pid;
        p->procinfo->ppid = p->ppid;
        p->procinfo->max_vcores = max_vcores(p);
        p->procinfo->tsc_freq = system_timing.tsc_freq;
        p->procinfo->heap_bottom = (void*)UTEXT;
        /* 0'ing the arguments.  Some higher function will need to set them */
        memset(p->procinfo->argp, 0, sizeof(p->procinfo->argp));
        memset(p->procinfo->argbuf, 0, sizeof(p->procinfo->argbuf));
        memset(p->procinfo->res_grant, 0, sizeof(p->procinfo->res_grant));
        /* 0'ing the vcore/pcore map.  Will link the vcores later. */
        memset(&p->procinfo->vcoremap, 0, sizeof(p->procinfo->vcoremap));
        memset(&p->procinfo->pcoremap, 0, sizeof(p->procinfo->pcoremap));
        p->procinfo->num_vcores = 0;
        p->procinfo->is_mcp = FALSE;
        p->procinfo->coremap_seqctr = SEQCTR_INITIALIZER;
        /* For now, we'll go up to the max num_cpus (at runtime).  In the future,
         * there may be cases where we can have more vcores than num_cpus, but for
         * now we'll leave it like this. */
        for (int i = 0; i < num_cpus; i++) {
                TAILQ_INSERT_TAIL(&p->inactive_vcs, &p->procinfo->vcoremap[i], list);
        }
}

static void proc_init_procdata(struct proc *p)
{
        memset(p->procdata, 0, sizeof(struct procdata));
        /* processes can't go into vc context on vc 0 til they unset this.  This is
         * for processes that block before initing uthread code (like rtld). */
        atomic_set(&p->procdata->vcore_preempt_data[0].flags, VC_SCP_NOVCCTX);
}

/* Allocates and initializes a process, with the given parent.  Currently
 * writes the *p into **pp, and returns 0 on success, < 0 for an error.
 * Errors include:
 *  - ENOFREEPID if it can't get a PID
 *  - ENOMEM on memory exhaustion */
error_t proc_alloc(struct proc **pp, struct proc *parent)
{
        error_t r;
        struct proc *p;

        if (!(p = kmem_cache_alloc(proc_cache, 0)))
                return -ENOMEM;

        { INITSTRUCT(*p)

        /* only one ref, which we pass back.  the old 'existence' ref is managed by
         * the ksched */
        kref_init(&p->p_kref, __proc_free, 1);
        // Setup the default map of where to get cache colors from
        p->cache_colors_map = global_cache_colors_map;
        p->next_cache_color = 0;
        /* Initialize the address space */
        if ((r = env_setup_vm(p)) < 0) {
                kmem_cache_free(proc_cache, p);
                return r;
        }
        if (!(p->pid = get_free_pid())) {
                kmem_cache_free(proc_cache, p);
                return -ENOFREEPID;
        }
        /* Set the basic status variables. */
        spinlock_init(&p->proc_lock);
        p->exitcode = 1337;     /* so we can see processes killed by the kernel */
        init_sem(&p->state_change, 0);
        p->ppid = parent ? parent->pid : 0;
        p->state = PROC_CREATED; /* shouldn't go through state machine for init */
        p->env_flags = 0;
        p->env_entry = 0; // cheating.  this really gets set later
        p->heap_top = (void*)UTEXT;     /* heap_bottom set in proc_init_procinfo */
        memset(&p->env_ancillary_state, 0, sizeof(p->env_ancillary_state));
        memset(&p->env_tf, 0, sizeof(p->env_tf));
        spinlock_init(&p->mm_lock);
        TAILQ_INIT(&p->vm_regions); /* could init this in the slab */
        /* Initialize the vcore lists, we'll build the inactive list so that it includes
         * all vcores when we initialize procinfo.  Do this before initing procinfo. */
        TAILQ_INIT(&p->online_vcs);
        TAILQ_INIT(&p->bulk_preempted_vcs);
        TAILQ_INIT(&p->inactive_vcs);
        /* Init procinfo/procdata.  Procinfo's argp/argb are 0'd */
        proc_init_procinfo(p);
        proc_init_procdata(p);

        /* Initialize the generic sysevent ring buffer */
        SHARED_RING_INIT(&p->procdata->syseventring);
        /* Initialize the frontend of the sysevent ring buffer */
        FRONT_RING_INIT(&p->syseventfrontring,
                        &p->procdata->syseventring,
                        SYSEVENTRINGSIZE);

        /* Init FS structures TODO: cleanup (might pull this out) */
        kref_get(&default_ns.kref, 1);
        p->ns = &default_ns;
        spinlock_init(&p->fs_env.lock);
        p->fs_env.umask = parent ? parent->fs_env.umask : S_IWGRP | S_IWOTH;
        p->fs_env.root = p->ns->root->mnt_root;
        kref_get(&p->fs_env.root->d_kref, 1);
        p->fs_env.pwd = parent ? parent->fs_env.pwd : p->fs_env.root;
        kref_get(&p->fs_env.pwd->d_kref, 1);
        memset(&p->open_files, 0, sizeof(p->open_files));       /* slightly ghetto */
        spinlock_init(&p->open_files.lock);
        p->open_files.max_files = NR_OPEN_FILES_DEFAULT;
        p->open_files.max_fdset = NR_FILE_DESC_DEFAULT;
        p->open_files.fd = p->open_files.fd_array;
        p->open_files.open_fds = (struct fd_set*)&p->open_files.open_fds_init;
        /* Init the ucq hash lock */
        p->ucq_hashlock = (struct hashlock*)&p->ucq_hl_noref;
        hashlock_init(p->ucq_hashlock, HASHLOCK_DEFAULT_SZ);

        atomic_inc(&num_envs);
        frontend_proc_init(p);
        printd("[%08x] new process %08x\n", current ? current->pid : 0, p->pid);
        } // INIT_STRUCT
        *pp = p;
        return 0;
}

/* We have a bunch of different ways to make processes.  Call this once the
 * process is ready to be used by the rest of the system.  For now, this just
 * means when it is ready to be named via the pidhash.  In the future, we might
 * push setting the state to CREATED into here. */
void __proc_ready(struct proc *p)
{
        /* Tell the ksched about us.  TODO: do we need to worry about the ksched
         * doing stuff to us before we're added to the pid_hash? */
        __sched_proc_register(p);
        spin_lock(&pid_hash_lock);
        hashtable_insert(pid_hash, (void*)(long)p->pid, p);
        spin_unlock(&pid_hash_lock);
}

/* Creates a process from the specified file, argvs, and envps.  Tempted to get
 * rid of proc_alloc's style, but it is so quaint... */
struct proc *proc_create(struct file *prog, char **argv, char **envp)
{
        struct proc *p;
        error_t r;
        if ((r = proc_alloc(&p, current)) < 0)
                panic("proc_create: %e", r);    /* one of 3 quaint usages of %e */
        procinfo_pack_args(p->procinfo, argv, envp);
        assert(load_elf(p, prog) == 0);
        /* Connect to stdin, stdout, stderr */
        assert(insert_file(&p->open_files, dev_stdin,  0) == 0);
        assert(insert_file(&p->open_files, dev_stdout, 0) == 1);
        assert(insert_file(&p->open_files, dev_stderr, 0) == 2);
        __proc_ready(p);
        return p;
}

/* This is called by kref_put(), once the last reference to the process is
 * gone.  Don't call this otherwise (it will panic).  It will clean up the
 * address space and deallocate any other used memory. */
static void __proc_free(struct kref *kref)
{
        struct proc *p = container_of(kref, struct proc, p_kref);
        physaddr_t pa;

        printd("[PID %d] freeing proc: %d\n", current ? current->pid : 0, p->pid);
        // All parts of the kernel should have decref'd before __proc_free is called
        assert(kref_refcnt(&p->p_kref) == 0);

        kref_put(&p->fs_env.root->d_kref);
        kref_put(&p->fs_env.pwd->d_kref);
        destroy_vmrs(p);
        frontend_proc_free(p);  /* TODO: please remove me one day */
        /* Free any colors allocated to this process */
        if (p->cache_colors_map != global_cache_colors_map) {
                for(int i = 0; i < llc_cache->num_colors; i++)
                        cache_color_free(llc_cache, p->cache_colors_map);
                cache_colors_map_free(p->cache_colors_map);
        }
        /* Remove us from the pid_hash and give our PID back (in that order). */
        spin_lock(&pid_hash_lock);
        if (!hashtable_remove(pid_hash, (void*)(long)p->pid))
                panic("Proc not in the pid table in %s", __FUNCTION__);
        spin_unlock(&pid_hash_lock);
        put_free_pid(p->pid);
        /* Flush all mapped pages in the user portion of the address space */
        env_user_mem_free(p, 0, UVPT);
        /* These need to be free again, since they were allocated with a refcnt. */
        free_cont_pages(p->procinfo, LOG2_UP(PROCINFO_NUM_PAGES));
        free_cont_pages(p->procdata, LOG2_UP(PROCDATA_NUM_PAGES));

        env_pagetable_free(p);
        p->env_pgdir = 0;
        p->env_cr3 = 0;

        atomic_dec(&num_envs);

        /* Dealloc the struct proc */
        kmem_cache_free(proc_cache, p);
}

/* Whether or not actor can control target.  Note we currently don't need
 * locking for this. TODO: think about that, esp wrt proc's dying. */
bool proc_controls(struct proc *actor, struct proc *target)
{
        return ((actor == target) || (target->ppid == actor->pid));
}

/* Helper to incref by val.  Using the helper to help debug/interpose on proc
 * ref counting.  Note that pid2proc doesn't use this interface. */
void proc_incref(struct proc *p, unsigned int val)
{
        kref_get(&p->p_kref, val);
}

/* Helper to decref for debugging.  Don't directly kref_put() for now. */
void proc_decref(struct proc *p)
{
        kref_put(&p->p_kref);
}

/* Helper, makes p the 'current' process, dropping the old current/cr3.  This no
 * longer assumes the passed in reference already counted 'current'.  It will
 * incref internally when needed. */
static void __set_proc_current(struct proc *p)
{
        /* We use the pcpui to access 'current' to cut down on the core_id() calls,
         * though who know how expensive/painful they are. */
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        /* If the process wasn't here, then we need to load its address space. */
        if (p != pcpui->cur_proc) {
                proc_incref(p, 1);
                lcr3(p->env_cr3);
                /* This is "leaving the process context" of the previous proc.  The
                 * previous lcr3 unloaded the previous proc's context.  This should
                 * rarely happen, since we usually proactively leave process context,
                 * but this is the fallback. */
                if (pcpui->cur_proc)
                        proc_decref(pcpui->cur_proc);
                pcpui->cur_proc = p;
        }
}

/* Flag says if vcore context is not ready, which is set in init_procdata.  The
 * process must turn off this flag on vcore0 at some point.  It's off by default
 * on all other vcores. */
static bool scp_is_vcctx_ready(struct preempt_data *vcpd)
{
        return !(atomic_read(&vcpd->flags) & VC_SCP_NOVCCTX);
}

/* Dispatches a _S process to run on the current core.  This should never be
 * called to "restart" a core.   
 *
 * This will always return, regardless of whether or not the calling core is
 * being given to a process. (it used to pop the tf directly, before we had
 * cur_tf).
 *
 * Since it always returns, it will never "eat" your reference (old
 * documentation talks about this a bit). */
void proc_run_s(struct proc *p)
{
        int8_t state = 0;
        uint32_t coreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        struct preempt_data *vcpd = &p->procdata->vcore_preempt_data[0];
        spin_lock(&p->proc_lock);
        switch (p->state) {
                case (PROC_DYING):
                        spin_unlock(&p->proc_lock);
                        printk("[kernel] _S %d not starting due to async death\n", p->pid);
                        return;
                case (PROC_RUNNABLE_S):
                        __proc_set_state(p, PROC_RUNNING_S);
                        /* We will want to know where this process is running, even if it is
                         * only in RUNNING_S.  can use the vcoremap, which makes death easy.
                         * Also, this is the signal used in trap.c to know to save the tf in
                         * env_tf. */
                        __seq_start_write(&p->procinfo->coremap_seqctr);
                        p->procinfo->num_vcores = 0;    /* TODO (VC#) */
                        /* TODO: For now, we won't count this as an active vcore (on the
                         * lists).  This gets unmapped in resource.c and yield_s, and needs
                         * work. */
                        __map_vcore(p, 0, coreid); /* not treated like a true vcore */
                        __seq_end_write(&p->procinfo->coremap_seqctr);
                        /* incref, since we're saving a reference in owning proc later */
                        proc_incref(p, 1);
                        /* disable interrupts to protect cur_tf, owning_proc, and current */
                        disable_irqsave(&state);
                        /* wait til ints are disabled before unlocking, in case someone else
                         * grabs the lock and IPIs us before we get set up in cur_tf */
                        spin_unlock(&p->proc_lock);
                        /* redundant with proc_startcore, might be able to remove that one*/
                        __set_proc_current(p);
                        /* set us up as owning_proc.  ksched bug if there is already one,
                         * for now.  can simply clear_owning if we want to. */
                        assert(!pcpui->owning_proc);
                        pcpui->owning_proc = p;
                        pcpui->owning_vcoreid = 0; /* TODO (VC#) */
                        /* TODO: (HSS) set silly state here (__startcore does it instantly) */
                        /* similar to the old __startcore, start them in vcore context if
                         * they have notifs and aren't already in vcore context.  o/w, start
                         * them wherever they were before (could be either vc ctx or not) */
                        if (!vcpd->notif_disabled && vcpd->notif_pending
                                                  && scp_is_vcctx_ready(vcpd)) {
                                vcpd->notif_disabled = TRUE;
                                /* save the _S's tf in the notify slot, build and pop a new one
                                 * in actual/cur_tf. */
                                vcpd->notif_tf = p->env_tf;
                                pcpui->cur_tf = &pcpui->actual_tf;
                                memset(pcpui->cur_tf, 0, sizeof(struct trapframe));
                                proc_init_trapframe(pcpui->cur_tf, 0, p->env_entry,
                                                    vcpd->transition_stack);
                        } else {
                                /* If they have no transition stack, then they can't receive
                                 * events.  The most they are getting is a wakeup from the
                                 * kernel.  They won't even turn off notif_pending, so we'll do
                                 * that for them. */
                                if (!scp_is_vcctx_ready(vcpd))
                                        vcpd->notif_pending = FALSE;
                                /* this is one of the few times cur_tf != &actual_tf */
                                pcpui->cur_tf = &p->env_tf;
                        }
                        enable_irqsave(&state);
                        /* When the calling core idles, it'll call restartcore and run the
                         * _S process's context. */
                        return;
                default:
                        spin_unlock(&p->proc_lock);
                        panic("Invalid process state %p in %s()!!", p->state, __FUNCTION__);
        }
}

/* Helper: sends preempt messages to all vcores on the bulk preempt list, and
 * moves them to the inactive list. */
static void __send_bulkp_events(struct proc *p)
{
        struct vcore *vc_i, *vc_temp;
        struct event_msg preempt_msg = {0};
        /* Whenever we send msgs with the proc locked, we need at least 1 online */
        assert(!TAILQ_EMPTY(&p->online_vcs));
        /* Send preempt messages for any left on the BP list.  No need to set any
         * flags, it all was done on the real preempt.  Now we're just telling the
         * process about any that didn't get restarted and are still preempted. */
        TAILQ_FOREACH_SAFE(vc_i, &p->bulk_preempted_vcs, list, vc_temp) {
                /* Note that if there are no active vcores, send_k_e will post to our
                 * own vcore, the last of which will be put on the inactive list and be
                 * the first to be started.  We could have issues with deadlocking,
                 * since send_k_e() could grab the proclock (if there are no active
                 * vcores) */
                preempt_msg.ev_type = EV_VCORE_PREEMPT;
                preempt_msg.ev_arg2 = vcore2vcoreid(p, vc_i);   /* arg2 is 32 bits */
                send_kernel_event(p, &preempt_msg, 0);
                /* TODO: we may want a TAILQ_CONCAT_HEAD, or something that does that.
                 * We need a loop for the messages, but not necessarily for the list
                 * changes.  */
                TAILQ_REMOVE(&p->bulk_preempted_vcs, vc_i, list);
                TAILQ_INSERT_HEAD(&p->inactive_vcs, vc_i, list);
        }
}

/* Run an _M.  Can be called safely on one that is already running.  Hold the
 * lock before calling.  Other than state checks, this just starts up the _M's
 * vcores, much like the second part of give_cores_running.  More specifically,
 * give_cores_runnable puts cores on the online list, which this then sends
 * messages to.  give_cores_running immediately puts them on the list and sends
 * the message.  the two-step style may go out of fashion soon.
 *
 * This expects that the "instructions" for which core(s) to run this on will be
 * in the vcoremap, which needs to be set externally (give_cores()). */
void __proc_run_m(struct proc *p)
{
        struct vcore *vc_i;
        switch (p->state) {
                case (PROC_WAITING):
                case (PROC_DYING):
                        warn("ksched tried to run proc %d in state %s\n", p->pid,
                             procstate2str(p->state));
                        return;
                case (PROC_RUNNABLE_M):
                        /* vcoremap[i] holds the coreid of the physical core allocated to
                         * this process.  It is set outside proc_run.  For the kernel
                         * message, a0 = struct proc*, a1 = struct trapframe*.   */
                        if (p->procinfo->num_vcores) {
                                __send_bulkp_events(p);
                                __proc_set_state(p, PROC_RUNNING_M);
                                /* Up the refcnt, to avoid the n refcnt upping on the
                                 * destination cores.  Keep in sync with __startcore */
                                proc_incref(p, p->procinfo->num_vcores * 2);
                                /* Send kernel messages to all online vcores (which were added
                                 * to the list and mapped in __proc_give_cores()), making them
                                 * turn online */
                                TAILQ_FOREACH(vc_i, &p->online_vcs, list) {
                                        send_kernel_message(vc_i->pcoreid, __startcore, (long)p,
                                                            (long)vcore2vcoreid(p, vc_i), 0,
                                                            KMSG_IMMEDIATE);
                                }
                        } else {
                                warn("Tried to proc_run() an _M with no vcores!");
                        }
                        /* There a subtle race avoidance here (when we unlock after sending
                         * the message).  __proc_startcore can handle a death message, but
                         * we can't have the startcore come after the death message.
                         * Otherwise, it would look like a new process.  So we hold the lock
                         * til after we send our message, which prevents a possible death
                         * message.
                         * - Note there is no guarantee this core's interrupts were on, so
                         *   it may not get the message for a while... */
                        return;
                case (PROC_RUNNING_M):
                        return;
                default:
                        /* unlock just so the monitor can call something that might lock*/
                        spin_unlock(&p->proc_lock);
                        panic("Invalid process state %p in %s()!!", p->state, __FUNCTION__);
        }
}

/* Actually runs the given context (trapframe) of process p on the core this
 * code executes on.  This is called directly by __startcore, which needs to
 * bypass the routine_kmsg check.  Interrupts should be off when you call this.
 *
 * A note on refcnting: this function will not return, and your proc reference
 * will end up stored in current.  This will make no changes to p's refcnt, so
 * do your accounting such that there is only the +1 for current.  This means if
 * it is already in current (like in the trap return path), don't up it.  If
 * it's already in current and you have another reference (like pid2proc or from
 * an IPI), then down it (which is what happens in __startcore()).  If it's not
 * in current and you have one reference, like proc_run(non_current_p), then
 * also do nothing.  The refcnt for your *p will count for the reference stored
 * in current. */
static void __proc_startcore(struct proc *p, trapframe_t *tf)
{
        assert(!irq_is_enabled());
        __set_proc_current(p);
        /* need to load our silly state, preferably somewhere other than here so we
         * can avoid the case where the context was just running here.  it's not
         * sufficient to do it in the "new process" if-block above (could be things
         * like page faults that cause us to keep the same process, but want a
         * different context.
         * for now, we load this silly state here. (TODO) (HSS)
         * We also need this to be per trapframe, and not per process...
         * For now / OSDI, only load it when in _S mode.  _M mode was handled in
         * __startcore.  */
        if (p->state == PROC_RUNNING_S)
                env_pop_ancillary_state(p);
        /* Clear the current_tf, since it is no longer used */
        current_tf = 0; /* TODO: might not need this... */
        env_pop_tf(tf);
}

/* Restarts/runs the current_tf, which must be for the current process, on the
 * core this code executes on.  Calls an internal function to do the work.
 *
 * In case there are pending routine messages, like __death, __preempt, or
 * __notify, we need to run them.  Alternatively, if there are any, we could
 * self_ipi, and run the messages immediately after popping back to userspace,
 * but that would have crappy overhead.
 *
 * Refcnting: this will not return, and it assumes that you've accounted for
 * your reference as if it was the ref for "current" (which is what happens when
 * returning from local traps and such. */
void proc_restartcore(void)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        assert(!pcpui->cur_sysc);
        /* TODO: can probably remove this enable_irq.  it was an optimization for
         * RKMs */
        /* Try and get any interrupts before we pop back to userspace.  If we didn't
         * do this, we'd just get them in userspace, but this might save us some
         * effort/overhead. */
        enable_irq();
        /* Need ints disabled when we return from processing (race on missing
         * messages/IPIs) */
        disable_irq();
        process_routine_kmsg(pcpui->cur_tf);
        /* If there is no owning process, just idle, since we don't know what to do.
         * This could be because the process had been restarted a long time ago and
         * has since left the core, or due to a KMSG like __preempt or __death. */
        if (!pcpui->owning_proc) {
                abandon_core();
                smp_idle();
        }
        assert(pcpui->cur_tf);
        __proc_startcore(pcpui->owning_proc, pcpui->cur_tf);
}

/* Destroys the process.  It will destroy the process and return any cores
 * to the ksched via the __sched_proc_destroy() CB.
 *
 * Here's the way process death works:
 * 0. grab the lock (protects state transition and core map)
 * 1. set state to dying.  that keeps the kernel from doing anything for the
 * process (like proc_running it).
 * 2. figure out where the process is running (cross-core/async or RUNNING_M)
 * 3. IPI to clean up those cores (decref, etc).
 * 4. Unlock
 * 5. Clean up your core, if applicable
 * (Last core/kernel thread to decref cleans up and deallocates resources.)
 *
 * Note that some cores can be processing async calls, but will eventually
 * decref.  Should think about this more, like some sort of callback/revocation.
 *
 * This function will now always return (it used to not return if the calling
 * core was dying).  However, when it returns, a kernel message will eventually
 * come in, making you abandon_core, as if you weren't running.  It may be that
 * the only reference to p is the one you passed in, and when you decref, it'll
 * get __proc_free()d. */
void proc_destroy(struct proc *p)
{
        uint32_t nr_cores_revoked = 0;
        struct kthread *sleeper;
        /* Can't spin on the proc lock with irq disabled.  This is a problem for all
         * places where we grab the lock, but it is particularly bad for destroy,
         * since we tend to call this from trap and irq handlers */
        assert(irq_is_enabled());
        spin_lock(&p->proc_lock);
        /* storage for pc_arr is alloced at decl, which is after grabbing the lock*/
        uint32_t pc_arr[p->procinfo->num_vcores];
        switch (p->state) {
                case PROC_DYING: /* someone else killed this already. */
                        spin_unlock(&p->proc_lock);
                        return;
                case PROC_CREATED:
                case PROC_RUNNABLE_S:
                case PROC_WAITING:
                        break;
                case PROC_RUNNABLE_M:
                case PROC_RUNNING_M:
                        /* Need to reclaim any cores this proc might have, even if it's not
                         * running yet.  Those running will receive a __death */
                        nr_cores_revoked = __proc_take_allcores(p, pc_arr, FALSE);
                        break;
                case PROC_RUNNING_S:
                        #if 0
                        // here's how to do it manually
                        if (current == p) {
                                lcr3(boot_cr3);
                                proc_decref(p);         /* this decref is for the cr3 */
                                current = NULL;
                        }
                        #endif
                        send_kernel_message(get_pcoreid(p, 0), __death, 0, 0, 0,
                                            KMSG_IMMEDIATE);
                        __seq_start_write(&p->procinfo->coremap_seqctr);
                        // TODO: might need to sort num_vcores too later (VC#)
                        /* vcore is unmapped on the receive side */
                        __seq_end_write(&p->procinfo->coremap_seqctr);
                        /* If we ever have RUNNING_S run on non-mgmt cores, we'll need to
                         * tell the ksched about this now-idle core (after unlocking) */
                        break;
                default:
                        warn("Weird state(%s) in %s()", procstate2str(p->state),
                             __FUNCTION__);
                        spin_unlock(&p->proc_lock);
                        return;
        }
        /* At this point, a death IPI should be on its way, either from the
         * RUNNING_S one, or from proc_take_cores with a __death.  in general,
         * interrupts should be on when you call proc_destroy locally, but currently
         * aren't for all things (like traphandlers). */
        __proc_set_state(p, PROC_DYING);
        spin_unlock(&p->proc_lock);
        /* This prevents processes from accessing their old files while dying, and
         * will help if these files (or similar objects in the future) hold
         * references to p (preventing a __proc_free()).  Need to unlock before
         * doing this - the proclock doesn't protect the files (not proc state), and
         * closing these might block (can't block while spinning). */
        /* TODO: might need some sync protection */
        close_all_files(&p->open_files, FALSE);
        /* Tell the ksched about our death, and which cores we freed up */
        __sched_proc_destroy(p, pc_arr, nr_cores_revoked);
        /* Signal our state change.  Assuming we only have one waiter right now. */
        sleeper = __up_sem(&p->state_change, TRUE);
        if (sleeper)
                kthread_runnable(sleeper);
}

/* Turns *p into an MCP.  Needs to be called from a local syscall of a RUNNING_S
 * process.  Returns 0 if it succeeded, an error code otherwise. */
int proc_change_to_m(struct proc *p)
{
        int retval = 0;
        int8_t state = 0;
        spin_lock(&p->proc_lock);
        /* in case userspace erroneously tries to change more than once */
        if (__proc_is_mcp(p))
                goto error_out;
        switch (p->state) {
                case (PROC_RUNNING_S):
                        /* issue with if we're async or not (need to preempt it)
                         * either of these should trip it. TODO: (ACR) async core req
                         * TODO: relies on vcore0 being the caller (VC#) */
                        if ((current != p) || (get_pcoreid(p, 0) != core_id()))
                                panic("We don't handle async RUNNING_S core requests yet.");
                        /* save the tf so userspace can restart it.  Like in __notify,
                         * this assumes a user tf is the same as a kernel tf.  We save
                         * it in the preempt slot so that we can also save the silly
                         * state. */
                        struct preempt_data *vcpd = &p->procdata->vcore_preempt_data[0];
                        disable_irqsave(&state);        /* protect cur_tf */
                        /* Note this won't play well with concurrent proc kmsgs, but
                         * since we're _S and locked, we shouldn't have any. */
                        assert(current_tf);
                        /* Copy uthread0's context to the notif slot */
                        vcpd->notif_tf = *current_tf;
                        clear_owning_proc(core_id());   /* so we don't restart */
                        save_fp_state(&vcpd->preempt_anc);
                        enable_irqsave(&state);
                        /* Userspace needs to not fuck with notif_disabled before
                         * transitioning to _M. */
                        if (vcpd->notif_disabled) {
                                printk("[kernel] user bug: notifs disabled for vcore 0\n");
                                vcpd->notif_disabled = FALSE;
                        }
                        /* in the async case, we'll need to remotely stop and bundle
                         * vcore0's TF.  this is already done for the sync case (local
                         * syscall). */
                        /* this process no longer runs on its old location (which is
                         * this core, for now, since we don't handle async calls) */
                        __seq_start_write(&p->procinfo->coremap_seqctr);
                        // TODO: (VC#) might need to adjust num_vcores
                        // TODO: (ACR) will need to unmap remotely (receive-side)
                        __unmap_vcore(p, 0);    /* VC# keep in sync with proc_run_s */
                        __seq_end_write(&p->procinfo->coremap_seqctr);
                        /* change to runnable_m (it's TF is already saved) */
                        __proc_set_state(p, PROC_RUNNABLE_M);
                        p->procinfo->is_mcp = TRUE;
                        spin_unlock(&p->proc_lock);
                        /* Tell the ksched that we're a real MCP now! */
                        __sched_proc_change_to_m(p);
                        return 0;
                case (PROC_RUNNABLE_S):
                        /* Issues: being on the runnable_list, proc_set_state not liking
                         * it, and not clearly thinking through how this would happen.
                         * Perhaps an async call that gets serviced after you're
                         * descheduled? */
                        warn("Not supporting RUNNABLE_S -> RUNNABLE_M yet.\n");
                        goto error_out;
                case (PROC_DYING):
                        warn("Dying, core request coming from %d\n", core_id());
                        goto error_out;
                default:
                        goto error_out;
        }
error_out:
        spin_unlock(&p->proc_lock);
        return -EINVAL;
}

/* Old code to turn a RUNNING_M to a RUNNING_S, with the calling context
 * becoming the new 'thread0'.  Don't use this.  Caller needs to send in a
 * pc_arr big enough for all vcores.  Will return the number of cores given up
 * by the proc. */
uint32_t __proc_change_to_s(struct proc *p, uint32_t *pc_arr)
{
        int8_t state = 0;
        uint32_t num_revoked;
        printk("[kernel] trying to transition _M -> _S (deprecated)!\n");
        assert(p->state == PROC_RUNNING_M); // TODO: (ACR) async core req
        /* save the context, to be restarted in _S mode */
        disable_irqsave(&state);        /* protect cur_tf */
        assert(current_tf);
        p->env_tf = *current_tf;
        clear_owning_proc(core_id());   /* so we don't restart */
        enable_irqsave(&state);
        env_push_ancillary_state(p); // TODO: (HSS)
        /* sending death, since it's not our job to save contexts or anything in
         * this case. */
        num_revoked = __proc_take_allcores(p, pc_arr, FALSE);
        __proc_set_state(p, PROC_RUNNABLE_S);
        return num_revoked;
}

/* Helper function.  Is the given pcore a mapped vcore?  No locking involved, be
 * careful. */
static bool is_mapped_vcore(struct proc *p, uint32_t pcoreid)
{
        return p->procinfo->pcoremap[pcoreid].valid;
}

/* Helper function.  Find the vcoreid for a given physical core id for proc p.
 * No locking involved, be careful.  Panics on failure. */
static uint32_t get_vcoreid(struct proc *p, uint32_t pcoreid)
{
        assert(is_mapped_vcore(p, pcoreid));
        return p->procinfo->pcoremap[pcoreid].vcoreid;
}

/* Helper function.  Try to find the pcoreid for a given virtual core id for
 * proc p.  No locking involved, be careful.  Use this when you can tolerate a
 * stale or otherwise 'wrong' answer. */
static uint32_t try_get_pcoreid(struct proc *p, uint32_t vcoreid)
{
        return p->procinfo->vcoremap[vcoreid].pcoreid;
}

/* Helper function.  Find the pcoreid for a given virtual core id for proc p.
 * No locking involved, be careful.  Panics on failure. */
static uint32_t get_pcoreid(struct proc *p, uint32_t vcoreid)
{
        assert(vcore_is_mapped(p, vcoreid));
        return try_get_pcoreid(p, vcoreid);
}

/* Helper: saves the SCP's tf state and unmaps vcore 0.  In the future, we'll
 * probably use vc0's space for env_tf and the silly state. */
void __proc_save_context_s(struct proc *p, struct trapframe *tf)
{
        p->env_tf= *tf;
        env_push_ancillary_state(p);                    /* TODO: (HSS) */
        __unmap_vcore(p, 0);    /* VC# keep in sync with proc_run_s */
}

/* Yields the calling core.  Must be called locally (not async) for now.
 * - If RUNNING_S, you just give up your time slice and will eventually return,
 *   possibly after WAITING on an event.
 * - If RUNNING_M, you give up the current vcore (which never returns), and
 *   adjust the amount of cores wanted/granted.
 * - If you have only one vcore, you switch to WAITING.  There's no 'classic
 *   yield' for MCPs (at least not now).  When you run again, you'll have one
 *   guaranteed core, starting from the entry point.
 *
 * If the call is being nice, it means different things for SCPs and MCPs.  For
 * MCPs, it means that it is in response to a preemption (which needs to be
 * checked).  If there is no preemption pending, just return.  For SCPs, it
 * means the proc wants to give up the core, but still has work to do.  If not,
 * the proc is trying to wait on an event.  It's not being nice to others, it
 * just has no work to do.
 *
 * This usually does not return (smp_idle()), so it will eat your reference.
 * Also note that it needs a non-current/edible reference, since it will abandon
 * and continue to use the *p (current == 0, no cr3, etc).
 *
 * We disable interrupts for most of it too, since we need to protect current_tf
 * and not race with __notify (which doesn't play well with concurrent
 * yielders). */
void proc_yield(struct proc *SAFE p, bool being_nice)
{
        uint32_t vcoreid, pcoreid = core_id();
        struct vcore *vc;
        struct preempt_data *vcpd;
        int8_t state = 0;
        /* Need to lock before checking the vcoremap to find out who we are, in case
         * we're getting __preempted and __startcored, from a remote core (in which
         * case we might have come in thinking we were vcore X, but had X preempted
         * and Y restarted on this pcore, and we suddenly are the wrong vcore
         * yielding).  Arguably, this is incredibly rare, since you'd need to
         * preempt the core, then decide to give it back with another grant in
         * between. */
        spin_lock(&p->proc_lock); /* horrible scalability.  =( */
        /* Need to disable before even reading vcoreid, since we could be unmapped
         * by a __preempt or __death.  _S also needs ints disabled, so we'll just do
         * it immediately.  Finally, we need to disable AFTER locking.  It is a bug
         * to grab the lock while irq's are disabled. */
        disable_irqsave(&state);
        switch (p->state) {
                case (PROC_RUNNING_S):
                        if (!being_nice) {
                                /* waiting for an event to unblock us */
                                vcpd = &p->procdata->vcore_preempt_data[0];
                                /* this check is an early optimization (check, signal, check
                                 * again pattern).  We could also lock before spamming the
                                 * vcore in event.c */
                                if (vcpd->notif_pending) {
                                        /* they can't handle events, just need to prevent a yield.
                                         * (note the notif_pendings are collapsed). */
                                        if (!scp_is_vcctx_ready(vcpd))
                                                vcpd->notif_pending = FALSE;
                                        goto out_failed;
                                }
                                /* syncing with event's SCP code.  we set waiting, then check
                                 * pending.  they set pending, then check waiting.  it's not
                                 * possible for us to miss the notif *and* for them to miss
                                 * WAITING.  one (or both) of us will see and make sure the proc
                                 * wakes up.  */
                                __proc_set_state(p, PROC_WAITING);
                                wrmb(); /* don't let the state write pass the notif read */ 
                                if (vcpd->notif_pending) {
                                        __proc_set_state(p, PROC_RUNNING_S);
                                        if (!scp_is_vcctx_ready(vcpd))
                                                vcpd->notif_pending = FALSE;
                                        goto out_failed;
                                }
                                /* if we're here, we want to sleep.  a concurrent event that
                                 * hasn't already written notif_pending will have seen WAITING,
                                 * and will be spinning while we do this. */
                                __proc_save_context_s(p, current_tf);
                                spin_unlock(&p->proc_lock);     /* note irqs are not enabled yet */
                        } else {
                                /* yielding to allow other processes to run.  we're briefly
                                 * WAITING, til we are woken up */
                                __proc_set_state(p, PROC_WAITING);
                                __proc_save_context_s(p, current_tf);
                                spin_unlock(&p->proc_lock);     /* note irqs are not enabled yet */
                                /* immediately wake up the proc (makes it runnable) */
                                proc_wakeup(p);
                        }
                        goto out_yield_core;
                case (PROC_RUNNING_M):
                        break;                          /* will handle this stuff below */
                case (PROC_DYING):              /* incoming __death */
                case (PROC_RUNNABLE_M): /* incoming (bulk) preempt/myield TODO:(BULK) */
                        goto out_failed;
                default:
                        panic("Weird state(%s) in %s()", procstate2str(p->state),
                              __FUNCTION__);
        }
        /* If we're already unmapped (__preempt or a __death was sent and the caller
         * unmapped us), bail out.  Note that if a __death hit us, we should have
         * bailed when we saw PROC_DYING.  Also note we might not have received the
         * __preempt or __death kmsg yet. */
        if (!is_mapped_vcore(p, pcoreid))
                goto out_failed;
        vcoreid = get_vcoreid(p, pcoreid);
        vc = vcoreid2vcore(p, vcoreid);
        vcpd = &p->procdata->vcore_preempt_data[vcoreid];
        /* no reason to be nice, return */
        if (being_nice && !vc->preempt_pending)
                goto out_failed;
        /* Sanity check, can remove after a while (we should have been unmapped) */
        assert(!vc->preempt_served);
        /* At this point, AFAIK there should be no preempt/death messages on the
         * way, and we're on the online list.  So we'll go ahead and do the yielding
         * business. */
        /* If there's a preempt pending, we don't need to preempt later since we are
         * yielding (nice or otherwise).  If not, this is just a regular yield. */
        if (vc->preempt_pending) {
                vc->preempt_pending = 0;
        } else {
                /* Optional: on a normal yield, check to see if we are putting them
                 * below amt_wanted (help with user races) and bail. */
                if (p->procdata->res_req[RES_CORES].amt_wanted >=
                                       p->procinfo->num_vcores)
                        goto out_failed;
        }
        /* Don't let them yield if they are missing a notification.  Userspace must
         * not leave vcore context without dealing with notif_pending.  pop_ros_tf()
         * handles leaving via uthread context.  This handles leaving via a yield.
         *
         * This early check is an optimization.  The real check is below when it
         * works with the online_vcs list (syncing with event.c and INDIR/IPI
         * posting). */
        if (vcpd->notif_pending)
                goto out_failed;
        /* Now we'll actually try to yield */
        printd("[K] Process %d (%p) is yielding on vcore %d\n", p->pid, p,
               get_vcoreid(p, coreid));
        /* Remove from the online list, add to the yielded list, and unmap
         * the vcore, which gives up the core. */
        TAILQ_REMOVE(&p->online_vcs, vc, list);
        /* Now that we're off the online list, check to see if an alert made
         * it through (event.c sets this) */
        wrmb(); /* prev write must hit before reading notif_pending */
        /* Note we need interrupts disabled, since a __notify can come in
         * and set pending to FALSE */
        if (vcpd->notif_pending) {
                /* We lost, put it back on the list and abort the yield */
                TAILQ_INSERT_TAIL(&p->online_vcs, vc, list); /* could go HEAD */
                goto out_failed;
        }
        /* We won the race with event sending, we can safely yield */
        TAILQ_INSERT_HEAD(&p->inactive_vcs, vc, list);
        /* Note this protects stuff userspace should look at, which doesn't
         * include the TAILQs. */
        __seq_start_write(&p->procinfo->coremap_seqctr);
        /* Next time the vcore starts, it starts fresh */
        vcpd->notif_disabled = FALSE;
        __unmap_vcore(p, vcoreid);
        p->procinfo->num_vcores--;
        p->procinfo->res_grant[RES_CORES] = p->procinfo->num_vcores;
        __seq_end_write(&p->procinfo->coremap_seqctr);
        /* No more vcores?  Then we wait on an event */
        if (p->procinfo->num_vcores == 0) {
                /* consider a ksched op to tell it about us WAITING */
                __proc_set_state(p, PROC_WAITING);
        }
        spin_unlock(&p->proc_lock);
        /* Hand the now-idle core to the ksched */
        __sched_put_idle_core(p, pcoreid);
        goto out_yield_core;
out_failed:
        /* for some reason we just want to return, either to take a KMSG that cleans
         * us up, or because we shouldn't yield (ex: notif_pending). */
        spin_unlock(&p->proc_lock);
        enable_irqsave(&state);
        return;
out_yield_core:                         /* successfully yielded the core */
        proc_decref(p);                 /* need to eat the ref passed in */
        /* Clean up the core and idle.  Need to do this before enabling interrupts,
         * since once we call __sched_put_idle_core(), we could get a startcore. */
        clear_owning_proc(pcoreid);     /* so we don't restart */
        abandon_core();
        smp_idle();                             /* will reenable interrupts */
}

/* Sends a notification (aka active notification, aka IPI) to p's vcore.  We
 * only send a notification if one they are enabled.  There's a bunch of weird
 * cases with this, and how pending / enabled are signals between the user and
 * kernel - check the documentation.  Note that pending is more about messages.
 * The process needs to be in vcore_context, and the reason is usually a
 * message.  We set pending here in case we were called to prod them into vcore
 * context (like via a sys_self_notify).  Also note that this works for _S
 * procs, if you send to vcore 0 (and the proc is running). */
void proc_notify(struct proc *p, uint32_t vcoreid)
{
        struct preempt_data *vcpd = &p->procdata->vcore_preempt_data[vcoreid];
        vcpd->notif_pending = TRUE;
        wrmb(); /* must write notif_pending before reading notif_disabled */
        if (!vcpd->notif_disabled) {
                /* GIANT WARNING: we aren't using the proc-lock to protect the
                 * vcoremap.  We want to be able to use this from interrupt context,
                 * and don't want the proc_lock to be an irqsave.  Spurious
                 * __notify() kmsgs are okay (it checks to see if the right receiver
                 * is current). */
                if (vcore_is_mapped(p, vcoreid)) {
                        printd("[kernel] sending notif to vcore %d\n", vcoreid);
                        /* This use of try_get_pcoreid is racy, might be unmapped */
                        send_kernel_message(try_get_pcoreid(p, vcoreid), __notify, (long)p,
                                            0, 0, KMSG_IMMEDIATE);
                }
        }
}

/* Makes sure p is runnable.  Callers may spam this, so it needs to handle
 * repeated calls for the same event.  Callers include event delivery, SCP
 * yield, and new SCPs.  Will trigger __sched_.cp_wakeup() CBs.  Will only
 * trigger the CB once, regardless of how many times we are called, *until* the
 * proc becomes WAITING again, presumably because of something the ksched did.*/
void proc_wakeup(struct proc *p)
{
        spin_lock(&p->proc_lock);
        if (__proc_is_mcp(p)) {
                /* we only wake up WAITING mcps */
                if (p->state != PROC_WAITING) {
                        spin_unlock(&p->proc_lock);
                        return;
                }
                __proc_set_state(p, PROC_RUNNABLE_M);
                spin_unlock(&p->proc_lock);
                __sched_mcp_wakeup(p);
                return;
        } else {
                /* SCPs can wake up for a variety of reasons.  the only times we need
                 * to do something is if it was waiting or just created.  other cases
                 * are either benign (just go out), or potential bugs (_Ms) */
                switch (p->state) {
                        case (PROC_CREATED):
                        case (PROC_WAITING):
                                __proc_set_state(p, PROC_RUNNABLE_S);
                                break;
                        case (PROC_RUNNABLE_S):
                        case (PROC_RUNNING_S):
                        case (PROC_DYING):
                                spin_unlock(&p->proc_lock);
                                return;
                        case (PROC_RUNNABLE_M):
                        case (PROC_RUNNING_M):
                                warn("Weird state(%s) in %s()", procstate2str(p->state),
                                     __FUNCTION__);
                                spin_unlock(&p->proc_lock);
                                return;
                }
                printd("[kernel] FYI, waking up an _S proc\n"); /* thanks, past brho! */
                spin_unlock(&p->proc_lock);
                __sched_scp_wakeup(p);
        }
}

/* Is the process in multi_mode / is an MCP or not?  */
bool __proc_is_mcp(struct proc *p)
{
        /* in lieu of using the amount of cores requested, or having a bunch of
         * states (like PROC_WAITING_M and _S), I'll just track it with a bool. */
        return p->procinfo->is_mcp;
}

/************************  Preemption Functions  ******************************
 * Don't rely on these much - I'll be sure to change them up a bit.
 *
 * Careful about what takes a vcoreid and what takes a pcoreid.  Also, there may
 * be weird glitches with setting the state to RUNNABLE_M.  It is somewhat in
 * flux.  The num_vcores is changed after take_cores, but some of the messages
 * (or local traps) may not yet be ready to handle seeing their future state.
 * But they should be, so fix those when they pop up.
 *
 * Another thing to do would be to make the _core functions take a pcorelist,
 * and not just one pcoreid. */

/* Sets a preempt_pending warning for p's vcore, to go off 'when'.  If you care
 * about locking, do it before calling.  Takes a vcoreid! */
void __proc_preempt_warn(struct proc *p, uint32_t vcoreid, uint64_t when)
{
        struct event_msg local_msg = {0};
        /* danger with doing this unlocked: preempt_pending is set, but never 0'd,
         * since it is unmapped and not dealt with (TODO)*/
        p->procinfo->vcoremap[vcoreid].preempt_pending = when;

        /* Send the event (which internally checks to see how they want it) */
        local_msg.ev_type = EV_PREEMPT_PENDING;
        local_msg.ev_arg1 = vcoreid;
        /* Whenever we send msgs with the proc locked, we need at least 1 online.
         * Caller needs to make sure the core was online/mapped. */
        assert(!TAILQ_EMPTY(&p->online_vcs));
        send_kernel_event(p, &local_msg, vcoreid);

        /* TODO: consider putting in some lookup place for the alarm to find it.
         * til then, it'll have to scan the vcoremap (O(n) instead of O(m)) */
}

/* Warns all active vcores of an impending preemption.  Hold the lock if you
 * care about the mapping (and you should). */
void __proc_preempt_warnall(struct proc *p, uint64_t when)
{
        struct vcore *vc_i;
        TAILQ_FOREACH(vc_i, &p->online_vcs, list)
                __proc_preempt_warn(p, vcore2vcoreid(p, vc_i), when);
        /* TODO: consider putting in some lookup place for the alarm to find it.
         * til then, it'll have to scan the vcoremap (O(n) instead of O(m)) */
}

// TODO: function to set an alarm, if none is outstanding

/* Raw function to preempt a single core.  If you care about locking, do it
 * before calling. */
void __proc_preempt_core(struct proc *p, uint32_t pcoreid)
{
        uint32_t vcoreid = get_vcoreid(p, pcoreid);
        struct event_msg preempt_msg = {0};
        p->procinfo->vcoremap[vcoreid].preempt_served = TRUE;
        // expects a pcorelist.  assumes pcore is mapped and running_m
        __proc_take_corelist(p, &pcoreid, 1, TRUE);
        /* Only send the message if we have an online core.  o/w, it would fuck
         * us up (deadlock), and hey don't need a message.  the core we just took
         * will be the first one to be restarted.  It will look like a notif.  in
         * the future, we could send the event if we want, but the caller needs to
         * do that (after unlocking). */
        if (!TAILQ_EMPTY(&p->online_vcs)) {
                preempt_msg.ev_type = EV_VCORE_PREEMPT;
                preempt_msg.ev_arg2 = vcoreid;
                send_kernel_event(p, &preempt_msg, 0);
        }
}

/* Raw function to preempt every vcore.  If you care about locking, do it before
 * calling. */
uint32_t __proc_preempt_all(struct proc *p, uint32_t *pc_arr)
{
        /* instead of doing this, we could just preempt_served all possible vcores,
         * and not just the active ones.  We would need to sort out a way to deal
         * with stale preempt_serveds first.  This might be just as fast anyways. */
        struct vcore *vc_i;
        /* TODO:(BULK) PREEMPT - don't bother with this, set a proc wide flag, or
         * just make us RUNNABLE_M.  Note this is also used by __map_vcore. */
        TAILQ_FOREACH(vc_i, &p->online_vcs, list)
                vc_i->preempt_served = TRUE;
        return __proc_take_allcores(p, pc_arr, TRUE);
}

/* Warns and preempts a vcore from p.  No delaying / alarming, or anything.  The
 * warning will be for u usec from now.  Returns TRUE if the core belonged to
 * the proc (and thus preempted), False if the proc no longer has the core. */
bool proc_preempt_core(struct proc *p, uint32_t pcoreid, uint64_t usec)
{
        uint64_t warn_time = read_tsc() + usec2tsc(usec);
        bool retval = FALSE;
        if (p->state != PROC_RUNNING_M) {
                /* more of an FYI for brho.  should be harmless to just return. */
                warn("Tried to preempt from a non RUNNING_M proc!");
                return FALSE;
        }
        spin_lock(&p->proc_lock);
        if (is_mapped_vcore(p, pcoreid)) {
                __proc_preempt_warn(p, get_vcoreid(p, pcoreid), warn_time);
                __proc_preempt_core(p, pcoreid);
                /* we might have taken the last core */
                if (!p->procinfo->num_vcores)
                        __proc_set_state(p, PROC_RUNNABLE_M);
                retval = TRUE;
        }
        spin_unlock(&p->proc_lock);
        return retval;
}

/* Warns and preempts all from p.  No delaying / alarming, or anything.  The
 * warning will be for u usec from now. */
void proc_preempt_all(struct proc *p, uint64_t usec)
{
        uint64_t warn_time = read_tsc() + usec2tsc(usec);
        uint32_t num_revoked = 0;
        spin_lock(&p->proc_lock);
        /* storage for pc_arr is alloced at decl, which is after grabbing the lock*/
        uint32_t pc_arr[p->procinfo->num_vcores];
        /* DYING could be okay */
        if (p->state != PROC_RUNNING_M) {
                warn("Tried to preempt from a non RUNNING_M proc!");
                spin_unlock(&p->proc_lock);
                return;
        }
        __proc_preempt_warnall(p, warn_time);
        num_revoked = __proc_preempt_all(p, pc_arr);
        assert(!p->procinfo->num_vcores);
        __proc_set_state(p, PROC_RUNNABLE_M);
        spin_unlock(&p->proc_lock);
        /* TODO: when we revise this func, look at __put_idle */
        /* Return the cores to the ksched */
        if (num_revoked)
                __sched_put_idle_cores(p, pc_arr, num_revoked);
}

/* Give the specific pcore to proc p.  Lots of assumptions, so don't really use
 * this.  The proc needs to be _M and prepared for it.  the pcore needs to be
 * free, etc. */
void proc_give(struct proc *p, uint32_t pcoreid)
{
        warn("Your idlecoremap is now screwed up");     /* TODO (IDLE) */
        spin_lock(&p->proc_lock);
        // expects a pcorelist, we give it a list of one
        __proc_give_cores(p, &pcoreid, 1);
        spin_unlock(&p->proc_lock);
}

/* Global version of the helper, for sys_get_vcoreid (might phase that syscall
 * out). */
uint32_t proc_get_vcoreid(struct proc *p)
{
        return per_cpu_info[core_id()].owning_vcoreid;
}

/* TODO: make all of these static inlines when we gut the env crap */
bool vcore_is_mapped(struct proc *p, uint32_t vcoreid)
{
        return p->procinfo->vcoremap[vcoreid].valid;
}

/* Can do this, or just create a new field and save it in the vcoremap */
uint32_t vcore2vcoreid(struct proc *p, struct vcore *vc)
{
        return (vc - p->procinfo->vcoremap);
}

struct vcore *vcoreid2vcore(struct proc *p, uint32_t vcoreid)
{
        return &p->procinfo->vcoremap[vcoreid];
}

/********** Core granting (bulk and single) ***********/

/* Helper: gives pcore to the process, mapping it to the next available vcore
 * from list vc_list.  Returns TRUE if we succeeded (non-empty).  If you pass in
 * **vc, we'll tell you which vcore it was. */
static bool __proc_give_a_pcore(struct proc *p, uint32_t pcore,
                                struct vcore_tailq *vc_list, struct vcore **vc)
{
        struct vcore *new_vc;
        new_vc = TAILQ_FIRST(vc_list);
        if (!new_vc)
                return FALSE;
        printd("setting vcore %d to pcore %d\n", vcore2vcoreid(p, new_vc),
               pcorelist[i]);
        TAILQ_REMOVE(vc_list, new_vc, list);
        TAILQ_INSERT_TAIL(&p->online_vcs, new_vc, list);
        __map_vcore(p, vcore2vcoreid(p, new_vc), pcore);
        if (vc)
                *vc = new_vc;
        return TRUE;
}

static void __proc_give_cores_runnable(struct proc *p, uint32_t *pc_arr,
                                       uint32_t num)
{
        assert(p->state == PROC_RUNNABLE_M);
        assert(num);    /* catch bugs */
        /* add new items to the vcoremap */
        __seq_start_write(&p->procinfo->coremap_seqctr);/* unncessary if offline */
        p->procinfo->num_vcores += num;
        for (int i = 0; i < num; i++) {
                /* Try from the bulk list first */
                if (__proc_give_a_pcore(p, pc_arr[i], &p->bulk_preempted_vcs, 0))
                        continue;
                /* o/w, try from the inactive list.  at one point, i thought there might
                 * be a legit way in which the inactive list could be empty, but that i
                 * wanted to catch it via an assert. */
                assert(__proc_give_a_pcore(p, pc_arr[i], &p->inactive_vcs, 0));
        }
        __seq_end_write(&p->procinfo->coremap_seqctr);
}

static void __proc_give_cores_running(struct proc *p, uint32_t *pc_arr,
                                      uint32_t num)
{
        struct vcore *vc_i;
        /* Up the refcnt, since num cores are going to start using this
         * process and have it loaded in their owning_proc and 'current'. */
        proc_incref(p, num * 2);        /* keep in sync with __startcore */
        __seq_start_write(&p->procinfo->coremap_seqctr);
        p->procinfo->num_vcores += num;
        assert(TAILQ_EMPTY(&p->bulk_preempted_vcs));
        for (int i = 0; i < num; i++) {
                assert(__proc_give_a_pcore(p, pc_arr[i], &p->inactive_vcs, &vc_i));
                send_kernel_message(pc_arr[i], __startcore, (long)p,
                                    (long)vcore2vcoreid(p, vc_i), 0, KMSG_IMMEDIATE);
        }
        __seq_end_write(&p->procinfo->coremap_seqctr);
}

/* Gives process p the additional num cores listed in pcorelist.  If the proc is
 * not RUNNABLE_M or RUNNING_M, this will fail and allocate none of the core
 * (and return -1).  If you're RUNNING_M, this will startup your new cores at
 * the entry point with their virtual IDs (or restore a preemption).  If you're
 * RUNNABLE_M, you should call __proc_run_m after this so that the process can
 * start to use its cores.  In either case, this returns 0.
 *
 * If you're *_S, make sure your core0's TF is set (which is done when coming in
 * via arch/trap.c and we are RUNNING_S), change your state, then call this.
 * Then call __proc_run_m().
 *
 * The reason I didn't bring the _S cases from core_request over here is so we
 * can keep this family of calls dealing with only *_Ms, to avoiding caring if
 * this is called from another core, and to avoid the _S -> _M transition.
 *
 * WARNING: You must hold the proc_lock before calling this! */
int __proc_give_cores(struct proc *p, uint32_t *pc_arr, uint32_t num)
{
        /* should never happen: */
        assert(num + p->procinfo->num_vcores <= MAX_NUM_CPUS);
        switch (p->state) {
                case (PROC_RUNNABLE_S):
                case (PROC_RUNNING_S):
                        warn("Don't give cores to a process in a *_S state!\n");
                        return -1;
                case (PROC_DYING):
                case (PROC_WAITING):
                        /* can't accept, just fail */
                        return -1;
                case (PROC_RUNNABLE_M):
                        __proc_give_cores_runnable(p, pc_arr, num);
                        break;
                case (PROC_RUNNING_M):
                        __proc_give_cores_running(p, pc_arr, num);
                        break;
                default:
                        panic("Weird state(%s) in %s()", procstate2str(p->state),
                              __FUNCTION__);
        }
        /* TODO: considering moving to the ksched (hard, due to yield) */
        p->procinfo->res_grant[RES_CORES] += num;
        return 0;
}

/********** Core revocation (bulk and single) ***********/

/* Revokes a single vcore from a process (unmaps or sends a KMSG to unmap). */
static void __proc_revoke_core(struct proc *p, uint32_t vcoreid, bool preempt)
{
        uint32_t pcoreid = get_pcoreid(p, vcoreid);
        struct preempt_data *vcpd;
        if (preempt) {
                /* Lock the vcore's state (necessary for preemption recovery) */
                vcpd = &p->procdata->vcore_preempt_data[vcoreid];
                atomic_or(&vcpd->flags, VC_K_LOCK);
                send_kernel_message(pcoreid, __preempt, (long)p, 0, 0, KMSG_IMMEDIATE);
        } else {
                send_kernel_message(pcoreid, __death, 0, 0, 0, KMSG_IMMEDIATE);
        }
}

/* Revokes all cores from the process (unmaps or sends a KMSGS). */
static void __proc_revoke_allcores(struct proc *p, bool preempt)
{
        struct vcore *vc_i;
        /* TODO: if we ever get broadcast messaging, use it here (still need to lock
         * the vcores' states for preemption) */
        TAILQ_FOREACH(vc_i, &p->online_vcs, list)
                __proc_revoke_core(p, vcore2vcoreid(p, vc_i), preempt);
}

/* Might be faster to scan the vcoremap than to walk the list... */
static void __proc_unmap_allcores(struct proc *p)
{
        struct vcore *vc_i;
        TAILQ_FOREACH(vc_i, &p->online_vcs, list)
                __unmap_vcore(p, vcore2vcoreid(p, vc_i));
}

/* Takes (revoke via kmsg or unmap) from process p the num cores listed in
 * pc_arr.  Will preempt if 'preempt' is set.  o/w, no state will be saved, etc.
 * Don't use this for taking all of a process's cores.
 *
 * Make sure you hold the lock when you call this, and make sure that the pcore
 * actually belongs to the proc, non-trivial due to other __preempt messages. */
void __proc_take_corelist(struct proc *p, uint32_t *pc_arr, uint32_t num,
                          bool preempt)
{
        struct vcore *vc;
        uint32_t vcoreid;
        assert(p->state & (PROC_RUNNING_M | PROC_RUNNABLE_M));
        __seq_start_write(&p->procinfo->coremap_seqctr);
        for (int i = 0; i < num; i++) {
                vcoreid = get_vcoreid(p, pc_arr[i]);
                /* Sanity check */
                assert(pc_arr[i] == get_pcoreid(p, vcoreid));
                /* Revoke / unmap core */
                if (p->state == PROC_RUNNING_M)
                        __proc_revoke_core(p, vcoreid, preempt);
                __unmap_vcore(p, vcoreid);
                /* Change lists for the vcore.  Note, the vcore is already unmapped
                 * and/or the messages are already in flight.  The only code that looks
                 * at the lists without holding the lock is event code. */
                vc = vcoreid2vcore(p, vcoreid);
                TAILQ_REMOVE(&p->online_vcs, vc, list);
                /* even for single preempts, we use the inactive list.  bulk preempt is
                 * only used for when we take everything. */
                TAILQ_INSERT_HEAD(&p->inactive_vcs, vc, list);
        }
        p->procinfo->num_vcores -= num;
        __seq_end_write(&p->procinfo->coremap_seqctr);
        p->procinfo->res_grant[RES_CORES] -= num;
}

/* Takes all cores from a process (revoke via kmsg or unmap), putting them on
 * the appropriate vcore list, and fills pc_arr with the pcores revoked, and
 * returns the number of entries in pc_arr.
 *
 * Make sure pc_arr is big enough to handle num_vcores().
 * Make sure you hold the lock when you call this. */
uint32_t __proc_take_allcores(struct proc *p, uint32_t *pc_arr, bool preempt)
{
        struct vcore *vc_i, *vc_temp;
        uint32_t num = 0;
        assert(p->state & (PROC_RUNNING_M | PROC_RUNNABLE_M));
        __seq_start_write(&p->procinfo->coremap_seqctr);
        /* Write out which pcores we're going to take */
        TAILQ_FOREACH(vc_i, &p->online_vcs, list)
                pc_arr[num++] = vc_i->pcoreid;
        /* Revoke if they are running, and unmap.  Both of these need the online
         * list to not be changed yet. */
        if (p->state == PROC_RUNNING_M)
                __proc_revoke_allcores(p, preempt);
        __proc_unmap_allcores(p);
        /* Move the vcores from online to the head of the appropriate list */
        TAILQ_FOREACH_SAFE(vc_i, &p->online_vcs, list, vc_temp) {
                /* TODO: we may want a TAILQ_CONCAT_HEAD, or something that does that */
                TAILQ_REMOVE(&p->online_vcs, vc_i, list);
                /* Put the cores on the appropriate list */
                if (preempt)
                        TAILQ_INSERT_HEAD(&p->bulk_preempted_vcs, vc_i, list);
                else
                        TAILQ_INSERT_HEAD(&p->inactive_vcs, vc_i, list);
        }
        assert(TAILQ_EMPTY(&p->online_vcs));
        assert(num == p->procinfo->num_vcores);
        p->procinfo->num_vcores = 0;
        __seq_end_write(&p->procinfo->coremap_seqctr);
        p->procinfo->res_grant[RES_CORES] = 0;
        return num;
}

/* Helper to do the vcore->pcore and inverse mapping.  Hold the lock when
 * calling. */
void __map_vcore(struct proc *p, uint32_t vcoreid, uint32_t pcoreid)
{
        /* Need to spin until __preempt is done saving state and whatnot before we
         * give the core back out.  Note that __preempt doesn't need the mapping: we
         * just need to not give out the same vcore (via a __startcore) until the
         * state is saved so __startcore has something to start. (and spinning in
         * startcore won't work, since startcore has no versioning). */
        while (p->procinfo->vcoremap[vcoreid].preempt_served)
                cpu_relax();
        p->procinfo->vcoremap[vcoreid].pcoreid = pcoreid;
        p->procinfo->vcoremap[vcoreid].valid = TRUE;
        p->procinfo->pcoremap[pcoreid].vcoreid = vcoreid;
        p->procinfo->pcoremap[pcoreid].valid = TRUE;
}

/* Helper to unmap the vcore->pcore and inverse mapping.  Hold the lock when
 * calling. */
void __unmap_vcore(struct proc *p, uint32_t vcoreid)
{
        p->procinfo->pcoremap[p->procinfo->vcoremap[vcoreid].pcoreid].valid = FALSE;
        p->procinfo->vcoremap[vcoreid].valid = FALSE;
}

/* Stop running whatever context is on this core and load a known-good cr3.
 * Note this leaves no trace of what was running. This "leaves the process's
 * context.  Also, we want interrupts disabled, to not conflict with kmsgs
 * (__launch_kthread, proc mgmt, etc).
 *
 * This does not clear the owning proc.  Use the other helper for that. */
void abandon_core(void)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        assert(!irq_is_enabled());
        /* Syscalls that don't return will ultimately call abadon_core(), so we need
         * to make sure we don't think we are still working on a syscall. */
        pcpui->cur_sysc = 0;
        if (pcpui->cur_proc)
                __abandon_core();
}

/* Helper to clear the core's owning processor and manage refcnting.  Pass in
 * core_id() to save a couple core_id() calls. */
void clear_owning_proc(uint32_t coreid)
{
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        struct proc *p = pcpui->owning_proc;
        assert(!irq_is_enabled());
        pcpui->owning_proc = 0;
        pcpui->owning_vcoreid = 0xdeadbeef;
        pcpui->cur_tf = 0;                      /* catch bugs for now (will go away soon) */
        if (p)
                proc_decref(p);
}

/* Switches to the address space/context of new_p, doing nothing if we are
 * already in new_p.  This won't add extra refcnts or anything, and needs to be
 * paired with switch_back() at the end of whatever function you are in.  Don't
 * migrate cores in the middle of a pair.  Specifically, the uncounted refs are
 * one for the old_proc, which is passed back to the caller, and new_p is
 * getting placed in cur_proc. */
struct proc *switch_to(struct proc *new_p)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        struct proc *old_proc;
        int8_t irq_state = 0;
        disable_irqsave(&irq_state);
        old_proc = pcpui->cur_proc;                                     /* uncounted ref */
        /* If we aren't the proc already, then switch to it */
        if (old_proc != new_p) {
                pcpui->cur_proc = new_p;                                /* uncounted ref */
                lcr3(new_p->env_cr3);
        }
        enable_irqsave(&irq_state);
        return old_proc;
}

/* This switches back to old_proc from new_p.  Pair it with switch_to(), and
 * pass in its return value for old_proc. */
void switch_back(struct proc *new_p, struct proc *old_proc)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        int8_t irq_state = 0;
        if (old_proc != new_p) {
                disable_irqsave(&irq_state);
                pcpui->cur_proc = old_proc;
                if (old_proc)
                        lcr3(old_proc->env_cr3);
                else
                        lcr3(boot_cr3);
                enable_irqsave(&irq_state);
        }
}

/* Will send a TLB shootdown message to every vcore in the main address space
 * (aka, all vcores for now).  The message will take the start and end virtual
 * addresses as well, in case we want to be more clever about how much we
 * shootdown and batching our messages.  Should do the sanity about rounding up
 * and down in this function too.
 *
 * Would be nice to have a broadcast kmsg at this point.  Note this may send a
 * message to the calling core (interrupting it, possibly while holding the
 * proc_lock).  We don't need to process routine messages since it's an
 * immediate message. */
void proc_tlbshootdown(struct proc *p, uintptr_t start, uintptr_t end)
{
        struct vcore *vc_i;
        /* TODO: we might be able to avoid locking here in the future (we must hit
         * all online, and we can check __mapped).  it'll be complicated. */
        spin_lock(&p->proc_lock);
        switch (p->state) {
                case (PROC_RUNNING_S):
                        tlbflush();
                        break;
                case (PROC_RUNNING_M):
                        /* TODO: (TLB) sanity checks and rounding on the ranges */
                        TAILQ_FOREACH(vc_i, &p->online_vcs, list) {
                                send_kernel_message(vc_i->pcoreid, __tlbshootdown, start, end,
                                                    0, KMSG_IMMEDIATE);
                        }
                        break;
                case (PROC_DYING):
                        /* if it is dying, death messages are already on the way to all
                         * cores, including ours, which will clear the TLB. */
                        break;
                default:
                        /* will probably get this when we have the short handlers */
                        warn("Unexpected case %s in %s", procstate2str(p->state),
                             __FUNCTION__);
        }
        spin_unlock(&p->proc_lock);
}

/* Helper, used by __startcore and change_to_vcore, which sets up cur_tf to run
 * a given process's vcore.  Caller needs to set up things like owning_proc and
 * whatnot.  Note that we might not have p loaded as current. */
static void __set_curtf_to_vcoreid(struct proc *p, uint32_t vcoreid)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        struct preempt_data *vcpd = &p->procdata->vcore_preempt_data[vcoreid];

        /* Mark that this vcore as no longer preempted.  No danger of clobbering
         * other writes, since this would get turned on in __preempt (which can't be
         * concurrent with this function on this core), and the atomic is just
         * toggling the one bit (a concurrent VC_K_LOCK will work) */
        atomic_and(&vcpd->flags, ~VC_PREEMPTED);
        /* Once the VC is no longer preempted, we allow it to receive msgs.  We
         * could let userspace do it, but handling it here makes it easier for them
         * to handle_indirs (when they turn this flag off).  Note the atomics
         * provide the needed barriers (cmb and mb on flags). */
        atomic_or(&vcpd->flags, VC_CAN_RCV_MSG);
        printd("[kernel] startcore on physical core %d for process %d's vcore %d\n",
               core_id(), p->pid, vcoreid);
        /* If notifs are disabled, the vcore was in vcore context and we need to
         * restart the preempt_tf.  o/w, we give them a fresh vcore (which is also
         * what happens the first time a vcore comes online).  No matter what,
         * they'll restart in vcore context.  It's just a matter of whether or not
         * it is the old, interrupted vcore context. */
        if (vcpd->notif_disabled) {
                restore_fp_state(&vcpd->preempt_anc);
                /* copy-in the tf we'll pop, then set all security-related fields */
                pcpui->actual_tf = vcpd->preempt_tf;
                proc_secure_trapframe(&pcpui->actual_tf);
        } else { /* not restarting from a preemption, use a fresh vcore */
                assert(vcpd->transition_stack);
                /* TODO: consider 0'ing the FP state.  We're probably leaking. */
                proc_init_trapframe(&pcpui->actual_tf, vcoreid, p->env_entry,
                                    vcpd->transition_stack);
                /* Disable/mask active notifications for fresh vcores */
                vcpd->notif_disabled = TRUE;
        }
        /* cur_tf was built above (in actual_tf), now use it */
        pcpui->cur_tf = &pcpui->actual_tf;
        /* this cur_tf will get run when the kernel returns / idles */
}

/* Changes calling vcore to be vcoreid.  enable_my_notif tells us about how the
 * state calling vcore wants to be left in.  It will look like caller_vcoreid
 * was preempted.  Note we don't care about notif_pending.
 *
 * Will return:
 *              0 if we successfully changed to the target vcore.
 *              -EBUSY if the target vcore is already mapped (a good kind of failure)
 *              -EAGAIN if we failed for some other reason and need to try again.  For
 *              example, the caller could be preempted, and we never even attempted to
 *              change.
 *              -EINVAL some userspace bug */
int proc_change_to_vcore(struct proc *p, uint32_t new_vcoreid,
                         bool enable_my_notif)
{
        uint32_t caller_vcoreid, pcoreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[pcoreid];
        struct preempt_data *caller_vcpd;
        struct vcore *caller_vc, *new_vc;
        struct event_msg preempt_msg = {0};
        int8_t state = 0;
        int retval = -EAGAIN;   /* by default, try again */
        /* Need to not reach outside the vcoremap, which might be smaller in the
         * future, but should always be as big as max_vcores */
        if (new_vcoreid >= p->procinfo->max_vcores)
                return -EINVAL;
        /* Need to lock before reading the vcoremap, like in yield.  Need to do this
         * before disabling irqs (deadlock with incoming proc mgmt kmsgs) */
        spin_lock(&p->proc_lock);
        /* Need to disable before even reading caller_vcoreid, since we could be
         * unmapped by a __preempt or __death, like in yield. */
        disable_irqsave(&state);
        /* new_vcoreid is already runing, abort */
        if (vcore_is_mapped(p, new_vcoreid)) {
                retval = -EBUSY;
                goto out_locked;
        }
        /* Need to make sure our vcore is allowed to switch.  We might have a
         * __preempt, __death, etc, coming in.  Similar to yield. */
        switch (p->state) {
                case (PROC_RUNNING_M):
                        break;                          /* the only case we can proceed */
                case (PROC_RUNNING_S):  /* user bug, just return */
                case (PROC_DYING):              /* incoming __death */
                case (PROC_RUNNABLE_M): /* incoming (bulk) preempt/myield TODO:(BULK) */
                        goto out_locked;
                default:
                        panic("Weird state(%s) in %s()", procstate2str(p->state),
                              __FUNCTION__);
        }
        /* Make sure we're still mapped in the proc. */
        if (!is_mapped_vcore(p, pcoreid))
                goto out_locked;
        /* Get all our info */
        caller_vcoreid = get_vcoreid(p, pcoreid);
        assert(caller_vcoreid == pcpui->owning_vcoreid);
        caller_vcpd = &p->procdata->vcore_preempt_data[caller_vcoreid];
        caller_vc = vcoreid2vcore(p, caller_vcoreid);
        /* Should only call from vcore context */
        if (!caller_vcpd->notif_disabled) {
                retval = -EINVAL;
                printk("[kernel] You tried to change vcores from uthread ctx\n");
                goto out_locked;
        }
        /* Sanity check, can remove after a while (we should have been unmapped) */
        assert(!caller_vc->preempt_served);
        /* Ok, we're clear to do the switch.  Lets figure out who the new one is */
        new_vc = vcoreid2vcore(p, new_vcoreid);
        printd("[kernel] changing vcore %d to vcore %d\n", caller_vcoreid,
               new_vcoreid);
        /* enable_my_notif signals how we'll be restarted */
        if (enable_my_notif) {
                /* if they set this flag, then the vcore can just restart from scratch,
                 * and we don't care about either the notif_tf or the preempt_tf. */
                caller_vcpd->notif_disabled = FALSE;
        } else {
                /* need to set up the calling vcore's tf so that it'll get restarted by
                 * __startcore, to make the caller look like it was preempted. */
                caller_vcpd->preempt_tf = *current_tf;
                save_fp_state(&caller_vcpd->preempt_anc);
                /* Mark our core as preempted (for userspace recovery). */
                atomic_or(&caller_vcpd->flags, VC_PREEMPTED);
        }
        /* Either way, unmap and offline our current vcore */
        /* Move the caller from online to inactive */
        TAILQ_REMOVE(&p->online_vcs, caller_vc, list);
        /* We don't bother with the notif_pending race.  note that notif_pending
         * could still be set.  this was a preempted vcore, and userspace will need
         * to deal with missed messages (preempt_recover() will handle that) */
        TAILQ_INSERT_HEAD(&p->inactive_vcs, caller_vc, list);
        /* Move the new one from inactive to online */
        TAILQ_REMOVE(&p->inactive_vcs, new_vc, list);
        TAILQ_INSERT_TAIL(&p->online_vcs, new_vc, list);
        /* Change the vcore map (TODO: might get rid of this seqctr) */
        __seq_start_write(&p->procinfo->coremap_seqctr);
        __unmap_vcore(p, caller_vcoreid);
        __map_vcore(p, new_vcoreid, pcoreid);
        __seq_end_write(&p->procinfo->coremap_seqctr);
        /* So this core knows which vcore is here: */
        pcpui->owning_vcoreid = new_vcoreid;
        /* Send either a PREEMPT msg or a CHECK_MSGS msg.  If they said to
         * enable_my_notif, then all userspace needs is to check messages, not a
         * full preemption recovery. */
        preempt_msg.ev_type = (enable_my_notif ? EV_CHECK_MSGS : EV_VCORE_PREEMPT);
        preempt_msg.ev_arg2 = caller_vcoreid;   /* arg2 is 32 bits */
        /* Whenever we send msgs with the proc locked, we need at least 1 online.
         * In this case, it's the one we just changed to. */
        assert(!TAILQ_EMPTY(&p->online_vcs));
        send_kernel_event(p, &preempt_msg, new_vcoreid);
        /* Change cur_tf so we'll be the new vcoreid */
        __set_curtf_to_vcoreid(p, new_vcoreid);
        retval = 0;
        /* Fall through to exit */
out_locked:
        spin_unlock(&p->proc_lock);
        enable_irqsave(&state);
        return retval;
}

/* Kernel message handler to start a process's context on this core, when the
 * core next considers running a process.  Tightly coupled with __proc_run_m().
 * Interrupts are disabled. */
void __startcore(struct trapframe *tf, uint32_t srcid, long a0, long a1, long a2)
{
        uint32_t vcoreid = (uint32_t)a1;
        uint32_t coreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        struct proc *p_to_run = (struct proc *CT(1))a0;

        assert(p_to_run);
        /* Can not be any TF from a process here already */
        assert(!pcpui->owning_proc);
        /* the sender of the amsg increfed already for this saved ref to p_to_run */
        pcpui->owning_proc = p_to_run;
        pcpui->owning_vcoreid = vcoreid;
        /* sender increfed again, assuming we'd install to cur_proc.  only do this
         * if no one else is there.  this is an optimization, since we expect to
         * send these __startcores to idles cores, and this saves a scramble to
         * incref when all of the cores restartcore/startcore later.  Keep in sync
         * with __proc_give_cores() and __proc_run_m(). */
        if (!pcpui->cur_proc) {
                pcpui->cur_proc = p_to_run;     /* install the ref to cur_proc */
                lcr3(p_to_run->env_cr3);        /* load the page tables to match cur_proc */
        } else {
                proc_decref(p_to_run);          /* can't install, decref the extra one */
        }
        /* Note we are not necessarily in the cr3 of p_to_run */
        /* Now that we sorted refcnts and know p / which vcore it should be, set up
         * pcpui->cur_tf so that it will run that particular vcore */
        __set_curtf_to_vcoreid(p_to_run, vcoreid);
}

/* Bail out if it's the wrong process, or if they no longer want a notif.  Don't
 * use the TF we passed in, we care about cur_tf.  Try not to grab locks or
 * write access to anything that isn't per-core in here. */
void __notify(struct trapframe *tf, uint32_t srcid, long a0, long a1, long a2)
{
        uint32_t vcoreid, coreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        struct preempt_data *vcpd;
        struct proc *p = (struct proc*)a0;

        /* Not the right proc */
        if (p != pcpui->owning_proc)
                return;
        /* Common cur_tf sanity checks.  Note cur_tf could be an _S's env_tf */
        assert(pcpui->cur_tf);
        assert(!in_kernel(pcpui->cur_tf));
        vcoreid = pcpui->owning_vcoreid;
        vcpd = &p->procdata->vcore_preempt_data[vcoreid];
        /* for SCPs that haven't (and might never) call vc_event_init, like rtld.
         * this is harmless for MCPS to check this */
        if (!scp_is_vcctx_ready(vcpd))
                return;
        printd("received active notification for proc %d's vcore %d on pcore %d\n",
               p->procinfo->pid, vcoreid, coreid);
        /* sort signals.  notifs are now masked, like an interrupt gate */
        if (vcpd->notif_disabled)
                return;
        vcpd->notif_disabled = TRUE;
        /* save the old tf in the notify slot, build and pop a new one.  Note that
         * silly state isn't our business for a notification. */
        vcpd->notif_tf = *pcpui->cur_tf;
        memset(pcpui->cur_tf, 0, sizeof(struct trapframe));
        proc_init_trapframe(pcpui->cur_tf, vcoreid, p->env_entry,
                            vcpd->transition_stack);
        /* this cur_tf will get run when the kernel returns / idles */
}

void __preempt(struct trapframe *tf, uint32_t srcid, long a0, long a1, long a2)
{
        uint32_t vcoreid, coreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        struct preempt_data *vcpd;
        struct proc *p = (struct proc*)a0;

        assert(p);
        if (p != pcpui->owning_proc) {
                panic("__preempt arrived for a process (%p) that was not owning (%p)!",
                      p, pcpui->owning_proc);
        }
        /* Common cur_tf sanity checks */
        assert(pcpui->cur_tf);
        assert(pcpui->cur_tf == &pcpui->actual_tf);
        assert(!in_kernel(pcpui->cur_tf));
        vcoreid = pcpui->owning_vcoreid;
        vcpd = &p->procdata->vcore_preempt_data[vcoreid];
        printd("[kernel] received __preempt for proc %d's vcore %d on pcore %d\n",
               p->procinfo->pid, vcoreid, coreid);
        /* if notifs are disabled, the vcore is in vcore context (as far as we're
         * concerned), and we save it in the preempt slot. o/w, we save the
         * process's cur_tf in the notif slot, and it'll appear to the vcore when it
         * comes back up that it just took a notification. */
        if (vcpd->notif_disabled)
                vcpd->preempt_tf = *pcpui->cur_tf;
        else
                vcpd->notif_tf = *pcpui->cur_tf;
        /* either way, we save the silly state (FP) */
        save_fp_state(&vcpd->preempt_anc);
        /* Mark the vcore as preempted and unlock (was locked by the sender). */
        atomic_or(&vcpd->flags, VC_PREEMPTED);
        atomic_and(&vcpd->flags, ~VC_K_LOCK);
        wmb();  /* make sure everything else hits before we finish the preempt */
        p->procinfo->vcoremap[vcoreid].preempt_served = FALSE;
        /* either __preempt or proc_yield() ends the preempt phase. */
        p->procinfo->vcoremap[vcoreid].preempt_pending = 0;
        /* We won't restart the process later.  current gets cleared later when we
         * notice there is no owning_proc and we have nothing to do (smp_idle,
         * restartcore, etc) */
        clear_owning_proc(coreid);
}

/* Kernel message handler to clean up the core when a process is dying.
 * Note this leaves no trace of what was running.
 * It's okay if death comes to a core that's already idling and has no current.
 * It could happen if a process decref'd before __proc_startcore could incref. */
void __death(struct trapframe *tf, uint32_t srcid, long a0, long a1, long a2)
{
        uint32_t vcoreid, coreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        struct proc *p = pcpui->owning_proc;
        if (p) {
                vcoreid = pcpui->owning_vcoreid;
                printd("[kernel] death on physical core %d for process %d's vcore %d\n",
                       coreid, p->pid, vcoreid);
                /* We won't restart the process later.  current gets cleared later when
                 * we notice there is no owning_proc and we have nothing to do
                 * (smp_idle, restartcore, etc) */
                clear_owning_proc(coreid);
        }
}

/* Kernel message handler, usually sent IMMEDIATE, to shoot down virtual
 * addresses from a0 to a1. */
void __tlbshootdown(struct trapframe *tf, uint32_t srcid, long a0, long a1,
                    long a2)
{
        /* TODO: (TLB) something more intelligent with the range */
        tlbflush();
}

void print_allpids(void)
{
        void print_proc_state(void *item)
        {
                struct proc *p = (struct proc*)item;
                assert(p);
                printk("%8d %s\n", p->pid, procstate2str(p->state));
        }
        printk("PID      STATE    \n");
        printk("------------------\n");
        spin_lock(&pid_hash_lock);
        hash_for_each(pid_hash, print_proc_state);
        spin_unlock(&pid_hash_lock);
}

void print_proc_info(pid_t pid)
{
        int j = 0;
        struct proc *p = pid2proc(pid);
        struct vcore *vc_i;
        if (!p) {
                printk("Bad PID.\n");
                return;
        }
        spinlock_debug(&p->proc_lock);
        //spin_lock(&p->proc_lock); // No locking!!
        printk("struct proc: %p\n", p);
        printk("PID: %d\n", p->pid);
        printk("PPID: %d\n", p->ppid);
        printk("State: %s (%p)\n", procstate2str(p->state), p->state);
        printk("Refcnt: %d\n", atomic_read(&p->p_kref.refcount) - 1);
        printk("Flags: 0x%08x\n", p->env_flags);
        printk("CR3(phys): 0x%08x\n", p->env_cr3);
        printk("Num Vcores: %d\n", p->procinfo->num_vcores);
        printk("Vcore Lists (may be in flux w/o locking):\n----------------------\n");
        printk("Online:\n");
        TAILQ_FOREACH(vc_i, &p->online_vcs, list)
                printk("\tVcore %d -> Pcore %d\n", vcore2vcoreid(p, vc_i), vc_i->pcoreid);
        printk("Bulk Preempted:\n");
        TAILQ_FOREACH(vc_i, &p->bulk_preempted_vcs, list)
                printk("\tVcore %d\n", vcore2vcoreid(p, vc_i));
        printk("Inactive / Yielded:\n");
        TAILQ_FOREACH(vc_i, &p->inactive_vcs, list)
                printk("\tVcore %d\n", vcore2vcoreid(p, vc_i));
        printk("Resources:\n------------------------\n");
        for (int i = 0; i < MAX_NUM_RESOURCES; i++)
                printk("\tRes type: %02d, amt wanted: %08d, amt granted: %08d\n", i,
                       p->procdata->res_req[i].amt_wanted, p->procinfo->res_grant[i]);
        printk("Open Files:\n");
        struct files_struct *files = &p->open_files;
        spin_lock(&files->lock);
        for (int i = 0; i < files->max_files; i++)
                if (files->fd_array[i].fd_file) {
                        printk("\tFD: %02d, File: %08p, File name: %s\n", i,
                               files->fd_array[i].fd_file,
                               file_name(files->fd_array[i].fd_file));
                }
        spin_unlock(&files->lock);
        /* No one cares, and it clutters the terminal */
        //printk("Vcore 0's Last Trapframe:\n");
        //print_trapframe(&p->env_tf);
        /* no locking / unlocking or refcnting */
        // spin_unlock(&p->proc_lock);
        proc_decref(p);
}

/* Debugging function, checks what (process, vcore) is supposed to run on this
 * pcore.  Meant to be called from smp_idle() before halting. */
void check_my_owner(void)
{
        struct per_cpu_info *pcpui = &per_cpu_info[core_id()];
        void shazbot(void *item)
        {
                struct proc *p = (struct proc*)item;
                struct vcore *vc_i;
                assert(p);
                spin_lock(&p->proc_lock);
                TAILQ_FOREACH(vc_i, &p->online_vcs, list) {
                        /* this isn't true, a __startcore could be on the way and we're
                         * already "online" */
                        if (vc_i->pcoreid == core_id()) {
                                /* Immediate message was sent, we should get it when we enable
                                 * interrupts, which should cause us to skip cpu_halt() */
                                if (!STAILQ_EMPTY(&pcpui->immed_amsgs))
                                        continue;
                                printk("Owned pcore (%d) has no owner, by %08p, vc %d!\n",
                                       core_id(), p, vcore2vcoreid(p, vc_i));
                                spin_unlock(&p->proc_lock);
                                spin_unlock(&pid_hash_lock);
                                monitor(0);
                        }
                }
                spin_unlock(&p->proc_lock);
        }
        assert(!irq_is_enabled());
        extern int booting;
        if (!booting && !pcpui->owning_proc) {
                spin_lock(&pid_hash_lock);
                hash_for_each(pid_hash, shazbot);
                spin_unlock(&pid_hash_lock);
        }
}