Fix extra decref of shared_page

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

/* Copyright (c) 2009, 2010 The Regents of the University of California
 * Barret Rhoden <brho@cs.berkeley.edu>
 * See LICENSE for details.
 *
 * Virtual memory management functions.  Creation, modification, etc, of virtual
 * memory regions (VMRs) as well as mmap(), mprotect(), and munmap().
 *
 * In general, error checking / bounds checks are done in the main function
 * (e.g. mmap()), and the work is done in a do_ function (e.g. do_mmap()).
 * Versions of those functions that are called when the vmr lock is already held
 * begin with __ (e.g. __do_munmap()).
 *
 * Note that if we were called from kern/src/syscall.c, we probably don't have
 * an edible reference to p. */

#include <frontend.h>
#include <ros/common.h>
#include <pmap.h>
#include <mm.h>
#include <process.h>
#include <stdio.h>
#include <syscall.h>
#include <slab.h>
#include <kmalloc.h>
#include <vfs.h>
#include <smp.h>
#include <profiler.h>

struct kmem_cache *vmr_kcache;

static int __vmr_free_pgs(struct proc *p, pte_t pte, void *va, void *arg);
static int populate_pm_va(struct proc *p, uintptr_t va, unsigned long nr_pgs,
                          int pte_prot, struct page_map *pm, size_t offset,
                          int flags, bool exec);

/* minor helper, will ease the file->chan transition */
static struct page_map *file2pm(struct file *file)
{
        return file->f_mapping;
}

void vmr_init(void)
{
        vmr_kcache = kmem_cache_create("vm_regions", sizeof(struct vm_region),
                                       __alignof__(struct dentry), 0, 0, 0);
}

/* For now, the caller will set the prot, flags, file, and offset.  In the
 * future, we may put those in here, to do clever things with merging vm_regions
 * that are the same.
 *
 * TODO: take a look at solari's vmem alloc.  And consider keeping these in a
 * tree of some sort for easier lookups. */
struct vm_region *create_vmr(struct proc *p, uintptr_t va, size_t len)
{
        struct vm_region *vmr = 0, *vm_i, *vm_next;
        uintptr_t gap_end;

        assert(!PGOFF(va));
        assert(!PGOFF(len));
        assert(va + len <= UMAPTOP);
        /* Is there room before the first one: */
        vm_i = TAILQ_FIRST(&p->vm_regions);
        /* This works for now, but if all we have is BRK_END ones, we'll start
         * growing backwards (TODO) */
        if (!vm_i || (va + len <= vm_i->vm_base)) {
                vmr = kmem_cache_alloc(vmr_kcache, 0);
                if (!vmr)
                        panic("EOM!");
                memset(vmr, 0, sizeof(struct vm_region));
                vmr->vm_base = va;
                TAILQ_INSERT_HEAD(&p->vm_regions, vmr, vm_link);
        } else {
                TAILQ_FOREACH(vm_i, &p->vm_regions, vm_link) {
                        vm_next = TAILQ_NEXT(vm_i, vm_link);
                        gap_end = vm_next ? vm_next->vm_base : UMAPTOP;
                        /* skip til we get past the 'hint' va */
                        if (va >= gap_end)
                                continue;
                        /* Find a gap that is big enough */
                        if (gap_end - vm_i->vm_end >= len) {
                                vmr = kmem_cache_alloc(vmr_kcache, 0);
                                if (!vmr)
                                        panic("EOM!");
                                memset(vmr, 0, sizeof(struct vm_region));
                                /* if we can put it at va, let's do that.  o/w, put it so it
                                 * fits */
                                if ((gap_end >= va + len) && (va >= vm_i->vm_end))
                                        vmr->vm_base = va;
                                else
                                        vmr->vm_base = vm_i->vm_end;
                                TAILQ_INSERT_AFTER(&p->vm_regions, vm_i, vmr, vm_link);
                                break;
                        }
                }
        }
        /* Finalize the creation, if we got one */
        if (vmr) {
                vmr->vm_proc = p;
                vmr->vm_end = vmr->vm_base + len;
        }
        if (!vmr)
                warn("Not making a VMR, wanted %p, + %p = %p", va, len, va + len);
        return vmr;
}

/* Split a VMR at va, returning the new VMR.  It is set up the same way, with
 * file offsets fixed accordingly.  'va' is the beginning of the new one, and
 * must be page aligned. */
struct vm_region *split_vmr(struct vm_region *old_vmr, uintptr_t va)
{
        struct vm_region *new_vmr;

        assert(!PGOFF(va));
        if ((old_vmr->vm_base >= va) || (old_vmr->vm_end <= va))
                return 0;
        new_vmr = kmem_cache_alloc(vmr_kcache, 0);
        TAILQ_INSERT_AFTER(&old_vmr->vm_proc->vm_regions, old_vmr, new_vmr,
                           vm_link);
        new_vmr->vm_proc = old_vmr->vm_proc;
        new_vmr->vm_base = va;
        new_vmr->vm_end = old_vmr->vm_end;
        old_vmr->vm_end = va;
        new_vmr->vm_prot = old_vmr->vm_prot;
        new_vmr->vm_flags = old_vmr->vm_flags;
        if (old_vmr->vm_file) {
                kref_get(&old_vmr->vm_file->f_kref, 1);
                new_vmr->vm_file = old_vmr->vm_file;
                new_vmr->vm_foff = old_vmr->vm_foff +
                                      old_vmr->vm_end - old_vmr->vm_base;
                pm_add_vmr(file2pm(old_vmr->vm_file), new_vmr);
        } else {
                new_vmr->vm_file = 0;
                new_vmr->vm_foff = 0;
        }
        return new_vmr;
}

/* Merges two vm regions.  For now, it will check to make sure they are the
 * same.  The second one will be destroyed. */
int merge_vmr(struct vm_region *first, struct vm_region *second)
{
        assert(first->vm_proc == second->vm_proc);
        if ((first->vm_end != second->vm_base) ||
            (first->vm_prot != second->vm_prot) ||
            (first->vm_flags != second->vm_flags) ||
            (first->vm_file != second->vm_file))
                return -1;
        if ((first->vm_file) && (second->vm_foff != first->vm_foff +
                                 first->vm_end - first->vm_base))
                return -1;
        first->vm_end = second->vm_end;
        destroy_vmr(second);
        return 0;
}

/* Attempts to merge vmr with adjacent VMRs, returning a ptr to be used for vmr.
 * It could be the same struct vmr, or possibly another one (usually lower in
 * the address space. */
struct vm_region *merge_me(struct vm_region *vmr)
{
        struct vm_region *vmr_temp;
        /* Merge will fail if it cannot do it.  If it succeeds, the second VMR is
         * destroyed, so we need to be a bit careful. */
        vmr_temp = TAILQ_PREV(vmr, vmr_tailq, vm_link);
        if (vmr_temp)
                if (!merge_vmr(vmr_temp, vmr))
                        vmr = vmr_temp;
        vmr_temp = TAILQ_NEXT(vmr, vm_link);
        if (vmr_temp)
                merge_vmr(vmr, vmr_temp);
        return vmr;
}

/* Grows the vm region up to (and not including) va.  Fails if another is in the
 * way, etc. */
int grow_vmr(struct vm_region *vmr, uintptr_t va)
{
        assert(!PGOFF(va));
        struct vm_region *next = TAILQ_NEXT(vmr, vm_link);
        if (next && next->vm_base < va)
                return -1;
        if (va <= vmr->vm_end)
                return -1;
        vmr->vm_end = va;
        return 0;
}

/* Shrinks the vm region down to (and not including) va.  Whoever calls this
 * will need to sort out the page table entries. */
int shrink_vmr(struct vm_region *vmr, uintptr_t va)
{
        assert(!PGOFF(va));
        if ((va < vmr->vm_base) || (va > vmr->vm_end))
                return -1;
        vmr->vm_end = va;
        return 0;
}

/* Called by the unmapper, just cleans up.  Whoever calls this will need to sort
 * out the page table entries. */
void destroy_vmr(struct vm_region *vmr)
{
        if (vmr->vm_file) {
                pm_remove_vmr(file2pm(vmr->vm_file), vmr);
                kref_put(&vmr->vm_file->f_kref);
        }
        TAILQ_REMOVE(&vmr->vm_proc->vm_regions, vmr, vm_link);
        kmem_cache_free(vmr_kcache, vmr);
}

/* Given a va and a proc (later an mm, possibly), returns the owning vmr, or 0
 * if there is none. */
struct vm_region *find_vmr(struct proc *p, uintptr_t va)
{
        struct vm_region *vmr;
        /* ugly linear seach */
        TAILQ_FOREACH(vmr, &p->vm_regions, vm_link) {
                if ((vmr->vm_base <= va) && (vmr->vm_end > va))
                        return vmr;
        }
        return 0;
}

/* Finds the first vmr after va (including the one holding va), or 0 if there is
 * none. */
struct vm_region *find_first_vmr(struct proc *p, uintptr_t va)
{
        struct vm_region *vmr;
        /* ugly linear seach */
        TAILQ_FOREACH(vmr, &p->vm_regions, vm_link) {
                if ((vmr->vm_base <= va) && (vmr->vm_end > va))
                        return vmr;
                if (vmr->vm_base > va)
                        return vmr;
        }
        return 0;
}

/* Makes sure that no VMRs cross either the start or end of the given region
 * [va, va + len), splitting any VMRs that are on the endpoints. */
void isolate_vmrs(struct proc *p, uintptr_t va, size_t len)
{
        struct vm_region *vmr;
        if ((vmr = find_vmr(p, va)))
                split_vmr(vmr, va);
        /* TODO: don't want to do another find (linear search) */
        if ((vmr = find_vmr(p, va + len)))
                split_vmr(vmr, va + len);
}

void unmap_and_destroy_vmrs(struct proc *p)
{
        struct vm_region *vmr_i, *vmr_temp;
        /* this only gets called from __proc_free, so there should be no sync
         * concerns.  still, better safe than sorry. */
        spin_lock(&p->vmr_lock);
        p->vmr_history++;
        spin_lock(&p->pte_lock);
        TAILQ_FOREACH(vmr_i, &p->vm_regions, vm_link) {
                /* note this CB sets the PTE = 0, regardless of if it was P or not */
                env_user_mem_walk(p, (void*)vmr_i->vm_base,
                                  vmr_i->vm_end - vmr_i->vm_base, __vmr_free_pgs, 0);
        }
        spin_unlock(&p->pte_lock);
        /* need the safe style, since destroy_vmr modifies the list.  also, we want
         * to do this outside the pte lock, since it grabs the pm lock. */
        TAILQ_FOREACH_SAFE(vmr_i, &p->vm_regions, vm_link, vmr_temp)
                destroy_vmr(vmr_i);
        spin_unlock(&p->vmr_lock);
}

/* Helper: copies the contents of pages from p to new p.  For pages that aren't
 * present, once we support swapping or CoW, we can do something more
 * intelligent.  0 on success, -ERROR on failure.  Can't handle jumbos. */
static int copy_pages(struct proc *p, struct proc *new_p, uintptr_t va_start,
                      uintptr_t va_end)
{
        /* Sanity checks.  If these fail, we had a screwed up VMR.
         * Check for: alignment, wraparound, or userspace addresses */
        if ((PGOFF(va_start)) ||
            (PGOFF(va_end)) ||
            (va_end < va_start) ||      /* now, start > UMAPTOP -> end > UMAPTOP */
            (va_end > UMAPTOP)) {
                warn("VMR mapping is probably screwed up (%p - %p)", va_start,
                     va_end);
                return -EINVAL;
        }
        int copy_page(struct proc *p, pte_t pte, void *va, void *arg) {
                struct proc *new_p = (struct proc*)arg;
                struct page *pp;
                if (pte_is_unmapped(pte))
                        return 0;
                /* pages could be !P, but right now that's only for file backed VMRs
                 * undergoing page removal, which isn't the caller of copy_pages. */
                if (pte_is_mapped(pte)) {
                        /* TODO: check for jumbos */
                        if (upage_alloc(new_p, &pp, 0))
                                return -ENOMEM;
                        memcpy(page2kva(pp), KADDR(pte_get_paddr(pte)), PGSIZE);
                        if (page_insert(new_p->env_pgdir, pp, va, pte_get_settings(pte))) {
                                page_decref(pp);
                                return -ENOMEM;
                        }
                } else if (pte_is_paged_out(pte)) {
                        /* TODO: (SWAP) will need to either make a copy or CoW/refcnt the
                         * backend store.  For now, this PTE will be the same as the
                         * original PTE */
                        panic("Swapping not supported!");
                } else {
                        panic("Weird PTE %p in %s!", pte_print(pte), __FUNCTION__);
                }
                return 0;
        }
        return env_user_mem_walk(p, (void*)va_start, va_end - va_start, &copy_page,
                                 new_p);
}

static int fill_vmr(struct proc *p, struct proc *new_p, struct vm_region *vmr)
{
        int ret = 0;

        if ((!vmr->vm_file) || (vmr->vm_flags & MAP_PRIVATE)) {
                assert(!(vmr->vm_flags & MAP_SHARED));
                ret = copy_pages(p, new_p, vmr->vm_base, vmr->vm_end);
        } else {
                /* non-private file, i.e. page cacheable.  we have to honor MAP_LOCKED,
                 * (but we might be able to ignore MAP_POPULATE). */
                if (vmr->vm_flags & MAP_LOCKED) {
                        /* need to keep the file alive in case we unlock/block */
                        kref_get(&vmr->vm_file->f_kref, 1);
                        /* math is a bit nasty if vm_base isn't page aligned */
                        assert(!PGOFF(vmr->vm_base));
                        ret = populate_pm_va(new_p, vmr->vm_base,
                                             (vmr->vm_end - vmr->vm_base) >> PGSHIFT,
                                             vmr->vm_prot, vmr->vm_file->f_mapping,
                                             vmr->vm_foff, vmr->vm_flags,
                                             vmr->vm_prot & PROT_EXEC);
                        kref_put(&vmr->vm_file->f_kref);
                }
        }
        return ret;
}

/* This will make new_p have the same VMRs as p, and it will make sure all
 * physical pages are copied over, with the exception of MAP_SHARED files.
 * MAP_SHARED files that are also MAP_LOCKED will be attached to the process -
 * presumably they are in the page cache since the parent locked them.  This is
 * all pretty nasty.
 *
 * This is used by fork().
 *
 * Note that if you are working on a VMR that is a file, you'll want to be
 * careful about how it is mapped (SHARED, PRIVATE, etc). */
int duplicate_vmrs(struct proc *p, struct proc *new_p)
{
        int ret = 0;
        struct vm_region *vmr, *vm_i;

        TAILQ_FOREACH(vm_i, &p->vm_regions, vm_link) {
                vmr = kmem_cache_alloc(vmr_kcache, 0);
                if (!vmr)
                        return -ENOMEM;
                vmr->vm_proc = new_p;
                vmr->vm_base = vm_i->vm_base;
                vmr->vm_end = vm_i->vm_end;
                vmr->vm_prot = vm_i->vm_prot;
                vmr->vm_flags = vm_i->vm_flags;
                vmr->vm_file = vm_i->vm_file;
                vmr->vm_foff = vm_i->vm_foff;
                if (vm_i->vm_file) {
                        kref_get(&vm_i->vm_file->f_kref, 1);
                        pm_add_vmr(file2pm(vm_i->vm_file), vmr);
                }
                ret = fill_vmr(p, new_p, vmr);
                if (ret) {
                        if (vm_i->vm_file) {
                                pm_remove_vmr(file2pm(vm_i->vm_file), vmr);
                                kref_put(&vm_i->vm_file->f_kref);
                        }
                        kmem_cache_free(vmr_kcache, vm_i);
                        return ret;
                }
                TAILQ_INSERT_TAIL(&new_p->vm_regions, vmr, vm_link);
        }
        return 0;
}

void print_vmrs(struct proc *p)
{
        int count = 0;
        struct vm_region *vmr;
        printk("VM Regions for proc %d\n", p->pid);
        printk("NR:"
               "                                     Range:"
               "       Prot,"
               "      Flags,"
               "               File,"
               "                Off\n");
        TAILQ_FOREACH(vmr, &p->vm_regions, vm_link)
                printk("%02d: (%p - %p): 0x%08x, 0x%08x, %p, %p\n", count++,
                       vmr->vm_base, vmr->vm_end, vmr->vm_prot, vmr->vm_flags,
                       vmr->vm_file, vmr->vm_foff);
}

void enumerate_vmrs(struct proc *p,
                                        void (*func)(struct vm_region *vmr, void *opaque),
                                        void *opaque)
{
        struct vm_region *vmr;

        spin_lock(&p->vmr_lock);
        TAILQ_FOREACH(vmr, &p->vm_regions, vm_link)
                func(vmr, opaque);
        spin_unlock(&p->vmr_lock);
}

/* Error values aren't quite comprehensive - check man mmap() once we do better
 * with the FS.
 *
 * The mmap call's offset is in units of PGSIZE (like Linux's mmap2()), but
 * internally, the offset is tracked in bytes.  The reason for the PGSIZE is for
 * 32bit apps to enumerate large files, but a full 64bit system won't need that.
 * We track things internally in bytes since that is how file pointers work, vmr
 * bases and ends, and similar math.  While it's not a hard change, there's no
 * need for it, and ideally we'll be a fully 64bit system before we deal with
 * files that large. */
void *mmap(struct proc *p, uintptr_t addr, size_t len, int prot, int flags,
           int fd, size_t offset)
{
        struct file *file = NULL;
        offset <<= PGSHIFT;
        printd("mmap(addr %x, len %x, prot %x, flags %x, fd %x, off %x)\n", addr,
               len, prot, flags, fd, offset);
        if (fd >= 0 && (flags & MAP_ANON)) {
                set_errno(EBADF);
                return MAP_FAILED;
        }
        if (!len) {
                set_errno(EINVAL);
                return MAP_FAILED;
        }
        if (fd != -1) {
                file = get_file_from_fd(&p->open_files, fd);
                if (!file) {
                        set_errno(EBADF);
                        return MAP_FAILED;
                }
        }
        /* Check for overflow.  This helps do_mmap and populate_va, among others. */
        if (offset + len < offset) {
                set_errno(EINVAL);
                return MAP_FAILED;
        }
        /* If they don't care where to put it, we'll start looking after the break.
         * We could just have userspace handle this (in glibc's mmap), so we don't
         * need to know about BRK_END, but this will work for now (and may avoid
         * bugs).  Note that this limits mmap(0) a bit.  Keep this in sync with
         * __do_mmap()'s check.  (Both are necessary).  */
        if (addr == 0)
                addr = BRK_END;
        /* Still need to enforce this: */
        addr = MAX(addr, MMAP_LOWEST_VA);
        /* Need to check addr + len, after we do our addr adjustments */
        if ((addr + len > UMAPTOP) || (PGOFF(addr))) {
                set_errno(EINVAL);
                return MAP_FAILED;
        }
        void *result = do_mmap(p, addr, len, prot, flags, file, offset);
        if (file)
                kref_put(&file->f_kref);
        return result;
}

/* Helper: returns TRUE if the VMR is allowed to access the file with prot.
 * This is a bit ghetto still: messes with the file mode and assumes it can walk
 * the dentry/inode paths without locking.  It also ignores the CoW stuff we'll
 * need to do eventually. */
static bool check_file_perms(struct vm_region *vmr, struct file *file, int prot)
{
        assert(file);
        if (prot & PROT_READ) {
                if (check_perms(file->f_dentry->d_inode, S_IRUSR))
                        goto out_error;
        }
        if (prot & PROT_WRITE) {
                /* if vmr maps a file as MAP_SHARED, then we need to make sure the
                 * protection change is in compliance with the open mode of the
                 * file. */
                if (vmr->vm_flags & MAP_SHARED) {
                        if (!(file->f_mode & S_IWUSR)) {
                                /* at this point, we have a file opened in the wrong mode,
                                 * but we may be allowed to access it still. */
                                if (check_perms(file->f_dentry->d_inode, S_IWUSR)) {
                                        goto out_error;
                                } else {
                                        /* it is okay, though we need to change the file mode. (note
                                         * the lack of a lock/protection (TODO) */
                                        file->f_mode |= S_IWUSR;
                                }
                        }
                } else {        /* PRIVATE mapping */
                        /* TODO: we want a CoW mapping (like we want in handle_page_fault()),
                         * since there is a concern of a process having the page already
                         * mapped in to a file it does not have permissions to, and then
                         * mprotecting it so it can access it.  So we can't just change
                         * the prot, and we don't know yet if a page is mapped in.  To
                         * handle this, we ought to sort out the CoW bit, and then this
                         * will be easy.  Til then, just do a permissions check.  If we
                         * start having weird issues with libc overwriting itself (since
                         * procs mprotect that W), then change this. */
                        if (check_perms(file->f_dentry->d_inode, S_IWUSR))
                                goto out_error;
                }
        }
        return TRUE;
out_error:      /* for debugging */
        printk("[kernel] mmap perm check failed for %s for access %d\n",
               file_name(file), prot);
        return FALSE;
}

/* Helper, maps in page at addr, but only if nothing is mapped there.  Returns
 * 0 on success.  If this is called by non-PM code, we'll store your ref in the
 * PTE. */
static int map_page_at_addr(struct proc *p, struct page *page, uintptr_t addr,
                            int prot)
{
        pte_t pte;
        spin_lock(&p->pte_lock);        /* walking and changing PTEs */
        /* find offending PTE (prob don't read this in).  This might alloc an
         * intermediate page table page. */
        pte = pgdir_walk(p->env_pgdir, (void*)addr, TRUE);
        if (!pte_walk_okay(pte)) {
                spin_unlock(&p->pte_lock);
                return -ENOMEM;
        }
        /* a spurious, valid PF is possible due to a legit race: the page might have
         * been faulted in by another core already (and raced on the memory lock),
         * in which case we should just return. */
        if (pte_is_present(pte)) {
                spin_unlock(&p->pte_lock);
                /* non-PM callers expect us to eat the ref if we succeed. */
                if (!page_is_pagemap(page))
                        page_decref(page);
                return 0;
        }
        if (pte_is_mapped(pte)) {
                /* we're clobbering an old entry.  if we're just updating the prot, then
                 * it's no big deal.  o/w, there might be an issue. */
                if (page2pa(page) != pte_get_paddr(pte)) {
                        warn_once("Clobbered a PTE mapping (%p -> %p)\n", pte_print(pte),
                                  page2pa(page) | prot);
                }
                if (!page_is_pagemap(pa2page(pte_get_paddr(pte))))
                        page_decref(pa2page(pte_get_paddr(pte)));
        }
        /* preserve the dirty bit - pm removal could be looking concurrently */
        prot |= (pte_is_dirty(pte) ? PTE_D : 0);
        /* We have a ref to page, which we are storing in the PTE */
        pte_write(pte, page2pa(page), prot);
        spin_unlock(&p->pte_lock);
        return 0;
}

/* Helper: copies *pp's contents to a new page, replacing your page pointer.  If
 * this succeeds, you'll have a non-PM page, which matters for how you put it.*/
static int __copy_and_swap_pmpg(struct proc *p, struct page **pp)
{
        struct page *new_page, *old_page = *pp;
        if (upage_alloc(p, &new_page, FALSE))
                return -ENOMEM;
        memcpy(page2kva(new_page), page2kva(old_page), PGSIZE);
        pm_put_page(old_page);
        *pp = new_page;
        return 0;
}

/* Hold the VMR lock when you call this - it'll assume the entire VA range is
 * mappable, which isn't true if there are concurrent changes to the VMRs. */
static int populate_anon_va(struct proc *p, uintptr_t va, unsigned long nr_pgs,
                            int pte_prot)
{
        struct page *page;
        int ret;
        for (long i = 0; i < nr_pgs; i++) {
                if (upage_alloc(p, &page, TRUE))
                        return -ENOMEM;
                /* could imagine doing a memwalk instead of a for loop */
                ret = map_page_at_addr(p, page, va + i * PGSIZE, pte_prot);
                if (ret) {
                        page_decref(page);
                        return ret;
                }
        }
        return 0;
}

/* This will periodically unlock the vmr lock. */
static int populate_pm_va(struct proc *p, uintptr_t va, unsigned long nr_pgs,
                          int pte_prot, struct page_map *pm, size_t offset,
                          int flags, bool exec)
{
        int ret = 0;
        unsigned long pm_idx0 = offset >> PGSHIFT;
        int vmr_history = ACCESS_ONCE(p->vmr_history);
        struct page *page;

        /* locking rules: start the loop holding the vmr lock, enter and exit the
         * entire func holding the lock. */
        for (long i = 0; i < nr_pgs; i++) {
                ret = pm_load_page_nowait(pm, pm_idx0 + i, &page);
                if (ret) {
                        if (ret != -EAGAIN)
                                break;
                        spin_unlock(&p->vmr_lock);
                        /* might block here, can't hold the spinlock */
                        ret = pm_load_page(pm, pm_idx0 + i, &page);
                        spin_lock(&p->vmr_lock);
                        if (ret)
                                break;
                        /* while we were sleeping, the VMRs could have changed on us. */
                        if (vmr_history != ACCESS_ONCE(p->vmr_history)) {
                                pm_put_page(page);
                                printk("[kernel] FYI: VMR changed during populate\n");
                                break;
                        }
                }
                if (flags & MAP_PRIVATE) {
                        ret = __copy_and_swap_pmpg(p, &page);
                        if (ret) {
                                pm_put_page(page);
                                break;
                        }
                }
                /* if this is an executable page, we might have to flush the
                 * instruction cache if our HW requires it.
                 * TODO: is this still needed?  andrew put this in a while ago*/
                if (exec)
                        icache_flush_page(0, page2kva(page));
                ret = map_page_at_addr(p, page, va + i * PGSIZE, pte_prot);
                if (page_is_pagemap(page))
                        pm_put_page(page);
                if (ret)
                        break;
        }
        return ret;
}

void *do_mmap(struct proc *p, uintptr_t addr, size_t len, int prot, int flags,
              struct file *file, size_t offset)
{
        len = ROUNDUP(len, PGSIZE);
        struct vm_region *vmr, *vmr_temp;

        /* read/write vmr lock (will change the tree) */
        spin_lock(&p->vmr_lock);
        p->vmr_history++;
        /* Sanity check, for callers that bypass mmap().  We want addr for anon
         * memory to start above the break limit (BRK_END), but not 0.  Keep this in
         * sync with BRK_END in mmap(). */
        if (addr == 0)
                addr = BRK_END;
        assert(!PGOFF(offset));

        /* MCPs will need their code and data pinned.  This check will start to fail
         * after uthread_slim_init(), at which point userspace should have enough
         * control over its mmaps (i.e. no longer done by LD or load_elf) that it
         * can ask for pinned and populated pages.  Except for dl_opens(). */
        struct preempt_data *vcpd = &p->procdata->vcore_preempt_data[0];
        if (file && (atomic_read(&vcpd->flags) & VC_SCP_NOVCCTX))
                flags |= MAP_POPULATE | MAP_LOCKED;
        /* Need to make sure nothing is in our way when we want a FIXED location.
         * We just need to split on the end points (if they exist), and then remove
         * everything in between.  __do_munmap() will do this.  Careful, this means
         * an mmap can be an implied munmap() (not my call...). */
        if (flags & MAP_FIXED)
                __do_munmap(p, addr, len);
        vmr = create_vmr(p, addr, len);
        if (!vmr) {
                printk("[kernel] do_mmap() aborted for %p + %d!\n", addr, len);
                set_errno(ENOMEM);
                spin_unlock(&p->vmr_lock);
                return MAP_FAILED;
        }
        addr = vmr->vm_base;
        vmr->vm_prot = prot;
        vmr->vm_flags = flags;
        vmr->vm_foff = offset;
        if (file) {
                if (!check_file_perms(vmr, file, prot)) {
                        assert(!vmr->vm_file);
                        destroy_vmr(vmr);
                        set_errno(EACCES);
                        spin_unlock(&p->vmr_lock);
                        return MAP_FAILED;
                }
                /* TODO: consider locking the file while checking (not as manadatory as
                 * in handle_page_fault() */
                if (nr_pages(offset + len) > nr_pages(file->f_dentry->d_inode->i_size)) {
                        /* We're allowing them to set up the VMR, though if they attempt to
                         * fault in any pages beyond the file's limit, they'll fail.  Since
                         * they might not access the region, we need to make sure POPULATE
                         * is off.  FYI, 64 bit glibc shared libs map in an extra 2MB of
                         * unaligned space between their RO and RW sections, but then
                         * immediately mprotect it to PROT_NONE. */
                        flags &= ~MAP_POPULATE;
                }
                /* Prep the FS to make sure it can mmap the file.  Slightly weird
                 * semantics: if we fail and had munmapped the space, they will have a
                 * hole in their VM now. */
                if (file->f_op->mmap(file, vmr)) {
                        assert(!vmr->vm_file);
                        destroy_vmr(vmr);
                        set_errno(EACCES);      /* not quite */
                        spin_unlock(&p->vmr_lock);
                        return MAP_FAILED;
                }
                kref_get(&file->f_kref, 1);
                pm_add_vmr(file2pm(file), vmr);
        }
        vmr->vm_file = file;
        vmr = merge_me(vmr);            /* attempts to merge with neighbors */

        if (flags & MAP_POPULATE && prot != PROT_NONE) {
                int pte_prot = (prot & PROT_WRITE) ? PTE_USER_RW :
                           (prot & (PROT_READ|PROT_EXEC)) ? PTE_USER_RO : 0;
                unsigned long nr_pgs = len >> PGSHIFT;
                int ret = 0;
                if (!file) {
                        ret = populate_anon_va(p, addr, nr_pgs, pte_prot);
                } else {
                        /* Note: this will unlock if it blocks.  our refcnt on the file
                         * keeps the pm alive when we unlock */
                        ret = populate_pm_va(p, addr, nr_pgs, pte_prot, file->f_mapping,
                                             offset, flags, prot & PROT_EXEC);
                }
                if (ret == -ENOMEM) {
                        spin_unlock(&p->vmr_lock);
                        printk("[kernel] ENOMEM, killing %d\n", p->pid);
                        proc_destroy(p);
                        return MAP_FAILED;      /* will never make it back to userspace */
                }
        }
        spin_unlock(&p->vmr_lock);

        profiler_notify_mmap(p, addr, len, prot, flags, file, offset);

        return (void*)addr;
}

int mprotect(struct proc *p, uintptr_t addr, size_t len, int prot)
{
        printd("mprotect: (addr %p, len %p, prot 0x%x)\n", addr, len, prot);
        if (!len)
                return 0;
        if ((addr % PGSIZE) || (addr < MMAP_LOWEST_VA)) {
                set_errno(EINVAL);
                return -1;
        }
        uintptr_t end = ROUNDUP(addr + len, PGSIZE);
        if (end > UMAPTOP || addr > end) {
                set_errno(ENOMEM);
                return -1;
        }
        /* read/write lock, will probably change the tree and settings */
        spin_lock(&p->vmr_lock);
        p->vmr_history++;
        int ret = __do_mprotect(p, addr, len, prot);
        spin_unlock(&p->vmr_lock);
        return ret;
}

/* This does not care if the region is not mapped.  POSIX says you should return
 * ENOMEM if any part of it is unmapped.  Can do this later if we care, based on
 * the VMRs, not the actual page residency. */
int __do_mprotect(struct proc *p, uintptr_t addr, size_t len, int prot)
{
        struct vm_region *vmr, *next_vmr;
        pte_t pte;
        bool shootdown_needed = FALSE;
        int pte_prot = (prot & PROT_WRITE) ? PTE_USER_RW :
                       (prot & (PROT_READ|PROT_EXEC)) ? PTE_USER_RO : PTE_NONE;
        /* TODO: this is aggressively splitting, when we might not need to if the
         * prots are the same as the previous.  Plus, there are three excessive
         * scans.  Finally, we might be able to merge when we are done. */
        isolate_vmrs(p, addr, len);
        vmr = find_first_vmr(p, addr);
        while (vmr && vmr->vm_base < addr + len) {
                if (vmr->vm_prot == prot)
                        continue;
                if (vmr->vm_file && !check_file_perms(vmr, vmr->vm_file, prot)) {
                        set_errno(EACCES);
                        return -1;
                }
                vmr->vm_prot = prot;
                spin_lock(&p->pte_lock);        /* walking and changing PTEs */
                /* TODO: use a memwalk.  At a minimum, we need to change every existing
                 * PTE that won't trigger a PF (meaning, present PTEs) to have the new
                 * prot.  The others will fault on access, and we'll change the PTE
                 * then.  In the off chance we have a mapped but not present PTE, we
                 * might as well change it too, since we're already here. */
                for (uintptr_t va = vmr->vm_base; va < vmr->vm_end; va += PGSIZE) {
                        pte = pgdir_walk(p->env_pgdir, (void*)va, 0);
                        if (pte_walk_okay(pte) && pte_is_mapped(pte)) {
                                pte_replace_perm(pte, pte_prot);
                                shootdown_needed = TRUE;
                        }
                }
                spin_unlock(&p->pte_lock);
                vmr = merge_me(vmr);
                next_vmr = TAILQ_NEXT(vmr, vm_link);
                vmr = next_vmr;
        }
        if (shootdown_needed)
                proc_tlbshootdown(p, addr, addr + len);
        return 0;
}

int munmap(struct proc *p, uintptr_t addr, size_t len)
{
        printd("munmap(addr %x, len %x)\n", addr, len);
        if (!len)
                return 0;
        len = ROUNDUP(len, PGSIZE);

        if ((addr % PGSIZE) || (addr < MMAP_LOWEST_VA)) {
                set_errno(EINVAL);
                return -1;
        }
        uintptr_t end = ROUNDUP(addr + len, PGSIZE);
        if (end > UMAPTOP || addr > end) {
                set_errno(EINVAL);
                return -1;
        }
        /* read/write: changing the vmrs (trees, properties, and whatnot) */
        spin_lock(&p->vmr_lock);
        p->vmr_history++;
        int ret = __do_munmap(p, addr, len);
        spin_unlock(&p->vmr_lock);
        return ret;
}

static int __munmap_mark_not_present(struct proc *p, pte_t pte, void *va,
                                     void *arg)
{
        bool *shootdown_needed = (bool*)arg;
        /* could put in some checks here for !P and also !0 */
        if (!pte_is_present(pte))       /* unmapped (== 0) *ptes are also not PTE_P */
                return 0;
        pte_clear_present(pte);
        *shootdown_needed = TRUE;
        return 0;
}

/* If our page is actually in the PM, we don't do anything.  All a page map
 * really needs is for our VMR to no longer track it (vmr being in the pm's
 * list) and to not point at its pages (mark it 0, dude).
 *
 * But private mappings mess with that a bit.  Luckily, we can tell by looking
 * at a page whether the specific page is in the PM or not.  If it isn't, we
 * still need to free our "VMR local" copy.
 *
 * For pages in a PM, we're racing with PM removers.  Both of us sync with the
 * mm lock, so once we hold the lock, it's a matter of whether or not the PTE is
 * 0 or not.  If it isn't, then we're still okay to look at the page.  Consider
 * the PTE a weak ref on the page.  So long as you hold the mm lock, you can
 * look at the PTE and know the page isn't being freed. */
static int __vmr_free_pgs(struct proc *p, pte_t pte, void *va, void *arg)
{
        struct page *page;
        if (pte_is_unmapped(pte))
                return 0;
        page = pa2page(pte_get_paddr(pte));
        pte_clear(pte);
        if (!page_is_pagemap(page))
                page_decref(page);
        return 0;
}

int __do_munmap(struct proc *p, uintptr_t addr, size_t len)
{
        struct vm_region *vmr, *next_vmr, *first_vmr;
        bool shootdown_needed = FALSE;

        /* TODO: this will be a bit slow, since we end up doing three linear
         * searches (two in isolate, one in find_first). */
        isolate_vmrs(p, addr, len);
        first_vmr = find_first_vmr(p, addr);
        vmr = first_vmr;
        spin_lock(&p->pte_lock);        /* changing PTEs */
        while (vmr && vmr->vm_base < addr + len) {
                env_user_mem_walk(p, (void*)vmr->vm_base, vmr->vm_end - vmr->vm_base,
                                  __munmap_mark_not_present, &shootdown_needed);
                vmr = TAILQ_NEXT(vmr, vm_link);
        }
        spin_unlock(&p->pte_lock);
        /* we haven't freed the pages yet; still using the PTEs to store the them.
         * There should be no races with inserts/faults, since we still hold the mm
         * lock since the previous CB. */
        if (shootdown_needed)
                proc_tlbshootdown(p, addr, addr + len);
        vmr = first_vmr;
        while (vmr && vmr->vm_base < addr + len) {
                /* there is rarely more than one VMR in this loop.  o/w, we'll need to
                 * gather up the vmrs and destroy outside the pte_lock. */
                spin_lock(&p->pte_lock);        /* changing PTEs */
                env_user_mem_walk(p, (void*)vmr->vm_base, vmr->vm_end - vmr->vm_base,
                                      __vmr_free_pgs, 0);
                spin_unlock(&p->pte_lock);
                next_vmr = TAILQ_NEXT(vmr, vm_link);
                destroy_vmr(vmr);
                vmr = next_vmr;
        }
        return 0;
}

/* Helper - drop the page differently based on where it is from */
static void __put_page(struct page *page)
{
        if (page_is_pagemap(page))
                pm_put_page(page);
        else
                page_decref(page);
}

static int __hpf_load_page(struct proc *p, struct page_map *pm,
                           unsigned long idx, struct page **page, bool first)
{
        int ret = 0;
        int coreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[coreid];
        bool wake_scp = FALSE;
        spin_lock(&p->proc_lock);
        switch (p->state) {
                case (PROC_RUNNING_S):
                        wake_scp = TRUE;
                        __proc_set_state(p, PROC_WAITING);
                        /* it's possible for HPF to loop a few times; we can only save the
                         * first time, o/w we could clobber. */
                        if (first) {
                                __proc_save_context_s(p);
                                __proc_save_fpu_s(p);
                                /* We clear the owner, since userspace doesn't run here
                                 * anymore, but we won't abandon since the fault handler
                                 * still runs in our process. */
                                clear_owning_proc(coreid);
                        }
                        /* other notes: we don't currently need to tell the ksched
                         * we switched from running to waiting, though we probably
                         * will later for more generic scheds. */
                        break;
                case (PROC_RUNNABLE_M):
                case (PROC_RUNNING_M):
                        spin_unlock(&p->proc_lock);
                        return -EAGAIN; /* will get reflected back to userspace */
                case (PROC_DYING):
                case (PROC_DYING_ABORT):
                        spin_unlock(&p->proc_lock);
                        return -EINVAL;
                default:
                        /* shouldn't have any waitings, under the current yield style.  if
                         * this becomes an issue, we can branch on is_mcp(). */
                        printk("HPF unexpectecd state(%s)", procstate2str(p->state));
                        spin_unlock(&p->proc_lock);
                        return -EINVAL;
        }
        spin_unlock(&p->proc_lock);
        ret = pm_load_page(pm, idx, page);
        if (wake_scp)
                proc_wakeup(p);
        if (ret) {
                printk("load failed with ret %d\n", ret);
                return ret;
        }
        /* need to put our old ref, next time around HPF will get another. */
        pm_put_page(*page);
        return 0;
}

/* Returns 0 on success, or an appropriate -error code.
 *
 * Notes: if your TLB caches negative results, you'll need to flush the
 * appropriate tlb entry.  Also, you could have a weird race where a present PTE
 * faulted for a different reason (was mprotected on another core), and the
 * shootdown is on its way.  Userspace should have waited for the mprotect to
 * return before trying to write (or whatever), so we don't care and will fault
 * them. */
static int __hpf(struct proc *p, uintptr_t va, int prot, bool file_ok)
{
        struct vm_region *vmr;
        struct page *a_page;
        unsigned int f_idx;     /* index of the missing page in the file */
        int ret = 0;
        bool first = TRUE;
        va = ROUNDDOWN(va,PGSIZE);

refault:
        /* read access to the VMRs TODO: RCU */
        spin_lock(&p->vmr_lock);
        /* Check the vmr's protection */
        vmr = find_vmr(p, va);
        if (!vmr) {                                                     /* not mapped at all */
                printd("fault: %p not mapped\n", va);
                ret = -EFAULT;
                goto out;
        }
        if (!(vmr->vm_prot & prot)) {           /* wrong prots for this vmr */
                ret = -EPERM;
                goto out;
        }
        if (!vmr->vm_file) {
                /* No file - just want anonymous memory */
                if (upage_alloc(p, &a_page, TRUE)) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else {
                if (!file_ok)
                        return -EACCES;
                /* If this fails, either something got screwed up with the VMR, or the
                 * permissions changed after mmap/mprotect.  Either way, I want to know
                 * (though it's not critical). */
                if (!check_file_perms(vmr, vmr->vm_file, prot))
                        printk("[kernel] possible issue with VMR prots on file %s!\n",
                               file_name(vmr->vm_file));
                /* Load the file's page in the page cache.
                 * TODO: (BLK) Note, we are holding the mem lock!  We need to rewrite
                 * this stuff so we aren't hold the lock as excessively as we are, and
                 * such that we can block and resume later. */
                assert(!PGOFF(va - vmr->vm_base + vmr->vm_foff));
                f_idx = (va - vmr->vm_base + vmr->vm_foff) >> PGSHIFT;
                /* TODO: need some sort of lock on the file to deal with someone
                 * concurrently shrinking it.  Adding 1 to f_idx, since it is
                 * zero-indexed */
                if (f_idx + 1 > nr_pages(vmr->vm_file->f_dentry->d_inode->i_size)) {
                        /* We're asking for pages that don't exist in the file */
                        /* TODO: unlock the file */
                        ret = -ESPIPE; /* linux sends a SIGBUS at access time */
                        goto out;
                }
                ret = pm_load_page_nowait(vmr->vm_file->f_mapping, f_idx, &a_page);
                if (ret) {
                        if (ret != -EAGAIN)
                                goto out;
                        /* keep the file alive after we unlock */
                        kref_get(&vmr->vm_file->f_kref, 1);
                        spin_unlock(&p->vmr_lock);
                        ret = __hpf_load_page(p, vmr->vm_file->f_mapping, f_idx, &a_page,
                                              first);
                        first = FALSE;
                        kref_put(&vmr->vm_file->f_kref);
                        if (ret)
                                return ret;
                        goto refault;
                }
                /* If we want a private map, we'll preemptively give you a new page.  We
                 * used to just care if it was private and writable, but were running
                 * into issues with libc changing its mapping (map private, then
                 * mprotect to writable...)  In the future, we want to CoW this anyway,
                 * so it's not a big deal. */
                if ((vmr->vm_flags & MAP_PRIVATE)) {
                        ret = __copy_and_swap_pmpg(p, &a_page);
                        if (ret)
                                goto out_put_pg;
                }
                /* if this is an executable page, we might have to flush the instruction
                 * cache if our HW requires it. */
                if (vmr->vm_prot & PROT_EXEC)
                        icache_flush_page((void*)va, page2kva(a_page));
        }
        /* update the page table TODO: careful with MAP_PRIVATE etc.  might do this
         * separately (file, no file) */
        int pte_prot = (vmr->vm_prot & PROT_WRITE) ? PTE_USER_RW :
                       (vmr->vm_prot & (PROT_READ|PROT_EXEC)) ? PTE_USER_RO : 0;
        ret = map_page_at_addr(p, a_page, va, pte_prot);
        if (ret) {
                printd("map_page_at for %p fails with %d\n", va, ret);
        }
        /* fall through, even for errors */
out_put_pg:
        /* the VMR's existence in the PM (via the mmap) allows us to have PTE point
         * to a_page without it magically being reallocated.  For non-PM memory
         * (anon memory or private pages) we transferred the ref to the PTE. */
        if (page_is_pagemap(a_page))
                pm_put_page(a_page);
out:
        spin_unlock(&p->vmr_lock);
        return ret;
}

int handle_page_fault(struct proc *p, uintptr_t va, int prot)
{
        return __hpf(p, va, prot, TRUE);
}

int handle_page_fault_nofile(struct proc *p, uintptr_t va, int prot)
{
        return __hpf(p, va, prot, FALSE);
}

/* Attempts to populate the pages, as if there was a page faults.  Bails on
 * errors, and returns the number of pages populated.  */
unsigned long populate_va(struct proc *p, uintptr_t va, unsigned long nr_pgs)
{
        struct vm_region *vmr, vmr_copy;
        unsigned long nr_pgs_this_vmr;
        unsigned long nr_filled = 0;
        struct page *page;
        int pte_prot;
        int ret;

        /* we can screw around with ways to limit the find_vmr calls (can do the
         * next in line if we didn't unlock, etc., but i don't expect us to do this
         * for more than a single VMR in most cases. */
        spin_lock(&p->vmr_lock);
        while (nr_pgs) {
                vmr = find_vmr(p, va);
                if (!vmr)
                        break;
                if (vmr->vm_prot == PROT_NONE)
                        break;
                pte_prot = (vmr->vm_prot & PROT_WRITE) ? PTE_USER_RW :
                           (vmr->vm_prot & (PROT_READ|PROT_EXEC)) ? PTE_USER_RO : 0;
                nr_pgs_this_vmr = MIN(nr_pgs, (vmr->vm_end - va) >> PGSHIFT);
                if (!vmr->vm_file) {
                        if (populate_anon_va(p, va, nr_pgs_this_vmr, pte_prot)) {
                                /* on any error, we can just bail.  we might be underestimating
                                 * nr_filled. */
                                break;
                        }
                } else {
                        /* need to keep the file alive in case we unlock/block */
                        kref_get(&vmr->vm_file->f_kref, 1);
                        /* Regarding foff + (va - base): va - base < len, and foff + len
                         * does not over flow */
                        ret = populate_pm_va(p, va, nr_pgs_this_vmr, pte_prot,
                                             vmr->vm_file->f_mapping,
                                             vmr->vm_foff + (va - vmr->vm_base),
                                             vmr->vm_flags, vmr->vm_prot & PROT_EXEC);
                        kref_put(&vmr->vm_file->f_kref);
                        if (ret) {
                                /* we might have failed if the underlying file doesn't cover the
                                 * mmap window, depending on how we'll deal with truncation. */
                                break;
                        }
                }
                nr_filled += nr_pgs_this_vmr;
                va += nr_pgs_this_vmr << PGSHIFT;
                nr_pgs -= nr_pgs_this_vmr;
        }
        spin_unlock(&p->vmr_lock);
        return nr_filled;
}

/* Kernel Dynamic Memory Mappings */
uintptr_t dyn_vmap_llim = KERN_DYN_TOP;
spinlock_t dyn_vmap_lock = SPINLOCK_INITIALIZER;

/* Reserve space in the kernel dynamic memory map area */
uintptr_t get_vmap_segment(unsigned long num_pages)
{
        uintptr_t retval;
        spin_lock(&dyn_vmap_lock);
        retval = dyn_vmap_llim - num_pages * PGSIZE;
        if ((retval > ULIM) && (retval < KERN_DYN_TOP)) {
                dyn_vmap_llim = retval;
        } else {
                warn("[kernel] dynamic mapping failed!");
                retval = 0;
        }
        spin_unlock(&dyn_vmap_lock);
        return retval;
}

/* Give up your space.  Note this isn't supported yet */
uintptr_t put_vmap_segment(uintptr_t vaddr, unsigned long num_pages)
{
        /* TODO: use vmem regions for adjustable vmap segments */
        warn("Not implemented, leaking vmem space.\n");
        return 0;
}

/* Map a virtual address chunk to physical addresses.  Make sure you got a vmap
 * segment before actually trying to do the mapping.
 *
 * Careful with more than one 'page', since it will assume your physical pages
 * are also contiguous.  Most callers will only use one page.
 *
 * Finally, note that this does not care whether or not there are real pages
 * being mapped, and will not attempt to incref your page (if there is such a
 * thing).  Handle your own refcnting for pages. */
int map_vmap_segment(uintptr_t vaddr, uintptr_t paddr, unsigned long num_pages,
                     int perm)
{
        /* For now, we only handle the root pgdir, and not any of the other ones
         * (like for processes).  To do so, we'll need to insert into every pgdir,
         * and send tlb shootdowns to those that are active (which we don't track
         * yet). */
        extern int booting;
        assert(booting);

        /* TODO: (MM) you should lock on boot pgdir modifications.  A vm region lock
         * isn't enough, since there might be a race on outer levels of page tables.
         * For now, we'll just use the dyn_vmap_lock (which technically works). */
        spin_lock(&dyn_vmap_lock);
        pte_t pte;
#ifdef CONFIG_X86
        perm |= PTE_G;
#endif
        for (int i = 0; i < num_pages; i++) {
                pte = pgdir_walk(boot_pgdir, (void*)(vaddr + i * PGSIZE), 1);
                if (!pte_walk_okay(pte)) {
                        spin_unlock(&dyn_vmap_lock);
                        return -ENOMEM;
                }
                /* You probably should have unmapped first */
                if (pte_is_mapped(pte))
                        warn("Existing PTE value %p\n", pte_print(pte));
                pte_write(pte, paddr + i * PGSIZE, perm);
        }
        spin_unlock(&dyn_vmap_lock);
        return 0;
}

/* Unmaps / 0's the PTEs of a chunk of vaddr space */
int unmap_vmap_segment(uintptr_t vaddr, unsigned long num_pages)
{
        /* Not a big deal - won't need this til we do something with kthreads */
        warn("Incomplete, don't call this yet.");
        spin_lock(&dyn_vmap_lock);
        /* TODO: For all pgdirs */
        pte_t pte;
        for (int i = 0; i < num_pages; i++) {
                pte = pgdir_walk(boot_pgdir, (void*)(vaddr + i * PGSIZE), 1);
                if (pte_walk_okay(pte))
                        pte_clear(pte);
        }
        /* TODO: TLB shootdown.  Also note that the global flag is set on the PTE
         * (for x86 for now), which requires a global shootdown.  bigger issue is
         * the TLB shootdowns for multiple pgdirs.  We'll need to remove from every
         * pgdir, and send tlb shootdowns to those that are active (which we don't
         * track yet). */
        spin_unlock(&dyn_vmap_lock);
        return 0;
}

/* This can handle unaligned paddrs */
static uintptr_t vmap_pmem_flags(uintptr_t paddr, size_t nr_bytes, int flags)
{
        uintptr_t vaddr;
        unsigned long nr_pages;
        assert(nr_bytes && paddr);
        nr_bytes += PGOFF(paddr);
        nr_pages = ROUNDUP(nr_bytes, PGSIZE) >> PGSHIFT;
        vaddr = get_vmap_segment(nr_pages);
        if (!vaddr) {
                warn("Unable to get a vmap segment");   /* probably a bug */
                return 0;
        }
        /* it's not strictly necessary to drop paddr's pgoff, but it might save some
         * vmap heartache in the future. */
        if (map_vmap_segment(vaddr, PG_ADDR(paddr), nr_pages,
                             PTE_KERN_RW | flags)) {
                warn("Unable to map a vmap segment");   /* probably a bug */
                return 0;
        }
        return vaddr + PGOFF(paddr);
}

uintptr_t vmap_pmem(uintptr_t paddr, size_t nr_bytes)
{
        return vmap_pmem_flags(paddr, nr_bytes, 0);
}

uintptr_t vmap_pmem_nocache(uintptr_t paddr, size_t nr_bytes)
{
        return vmap_pmem_flags(paddr, nr_bytes, PTE_NOCACHE);
}

uintptr_t vmap_pmem_writecomb(uintptr_t paddr, size_t nr_bytes)
{
        return vmap_pmem_flags(paddr, nr_bytes, PTE_WRITECOMB);
}

int vunmap_vmem(uintptr_t vaddr, size_t nr_bytes)
{
        unsigned long nr_pages = ROUNDUP(nr_bytes, PGSIZE) >> PGSHIFT;
        unmap_vmap_segment(vaddr, nr_pages);
        put_vmap_segment(vaddr, nr_pages);
        return 0;
}