SSL userfaultfd.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
*  mm/userfaultfd.c
*
*  Copyright (C) 2015  Red Hat, Inc.
*/

#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/userfaultfd_k.h>
#include <linux/mmu_notifier.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>
#include "internal.h"
#include "swap.h"

static __always_inline
bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)
{
/* Make sure that the dst range is fully within dst_vma. */
if (dst_end > dst_vma->vm_end)
  return false;

/*
* Check the vma is registered in uffd, this is required to
* enforce the VM_MAYWRITE check done at uffd registration
* time.
*/
if (!dst_vma->vm_userfaultfd_ctx.ctx)
  return false;

return true;
}

static __always_inline
struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
       unsigned long addr)
{
struct vm_area_struct *vma;

mmap_assert_locked(mm);
vma = vma_lookup(mm, addr);
if (!vma)
  vma = ERR_PTR(-ENOENT);
else if (!(vma->vm_flags & VM_SHARED) &&
   unlikely(anon_vma_prepare(vma)))
  vma = ERR_PTR(-ENOMEM);

return vma;
}

#ifdef CONFIG_PER_VMA_LOCK
/*
* uffd_lock_vma() - Lookup and lock vma corresponding to @address.
* @mm: mm to search vma in.
* @address: address that the vma should contain.
*
* Should be called without holding mmap_lock.
*
* Return: A locked vma containing @address, -ENOENT if no vma is found, or
* -ENOMEM if anon_vma couldn't be allocated.
*/
static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
           unsigned long address)
{
struct vm_area_struct *vma;

vma = lock_vma_under_rcu(mm, address);
if (vma) {
  /*
* We know we're going to need to use anon_vma, so check
* that early.
*/
  if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
   vma_end_read(vma);
  else
   return vma;
}

mmap_read_lock(mm);
vma = find_vma_and_prepare_anon(mm, address);
if (!IS_ERR(vma)) {
  bool locked = vma_start_read_locked(vma);

  if (!locked)
   vma = ERR_PTR(-EAGAIN);
}

mmap_read_unlock(mm);
return vma;
}

static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
           unsigned long dst_start,
           unsigned long len)
{
struct vm_area_struct *dst_vma;

dst_vma = uffd_lock_vma(dst_mm, dst_start);
if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
  return dst_vma;

vma_end_read(dst_vma);
return ERR_PTR(-ENOENT);
}

static void uffd_mfill_unlock(struct vm_area_struct *vma)
{
vma_end_read(vma);
}

#else

static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
           unsigned long dst_start,
           unsigned long len)
{
struct vm_area_struct *dst_vma;

mmap_read_lock(dst_mm);
dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
if (IS_ERR(dst_vma))
  goto out_unlock;

if (validate_dst_vma(dst_vma, dst_start + len))
  return dst_vma;

dst_vma = ERR_PTR(-ENOENT);
out_unlock:
mmap_read_unlock(dst_mm);
return dst_vma;
}

static void uffd_mfill_unlock(struct vm_area_struct *vma)
{
mmap_read_unlock(vma->vm_mm);
}
#endif

/* Check if dst_addr is outside of file's size. Must be called with ptl held. */
static bool mfill_file_over_size(struct vm_area_struct *dst_vma,
     unsigned long dst_addr)
{
struct inode *inode;
pgoff_t offset, max_off;

if (!dst_vma->vm_file)
  return false;

inode = dst_vma->vm_file->f_inode;
offset = linear_page_index(dst_vma, dst_addr);
max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
return offset >= max_off;
}

/*
* Install PTEs, to map dst_addr (within dst_vma) to page.
*
* This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
* and anon, and for both shared and private VMAs.
*/
int mfill_atomic_install_pte(pmd_t *dst_pmd,
        struct vm_area_struct *dst_vma,
        unsigned long dst_addr, struct page *page,
        bool newly_allocated, uffd_flags_t flags)
{
int ret;
struct mm_struct *dst_mm = dst_vma->vm_mm;
pte_t _dst_pte, *dst_pte;
bool writable = dst_vma->vm_flags & VM_WRITE;
bool vm_shared = dst_vma->vm_flags & VM_SHARED;
spinlock_t *ptl;
struct folio *folio = page_folio(page);
bool page_in_cache = folio_mapping(folio);

_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
_dst_pte = pte_mkdirty(_dst_pte);
if (page_in_cache && !vm_shared)
  writable = false;
if (writable)
  _dst_pte = pte_mkwrite(_dst_pte, dst_vma);
if (flags & MFILL_ATOMIC_WP)
  _dst_pte = pte_mkuffd_wp(_dst_pte);

ret = -EAGAIN;
dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
if (!dst_pte)
  goto out;

if (mfill_file_over_size(dst_vma, dst_addr)) {
  ret = -EFAULT;
  goto out_unlock;
}

ret = -EEXIST;
/*
* We allow to overwrite a pte marker: consider when both MISSING|WP
* registered, we firstly wr-protect a none pte which has no page cache
* page backing it, then access the page.
*/
if (!pte_none_mostly(ptep_get(dst_pte)))
  goto out_unlock;

if (page_in_cache) {
  /* Usually, cache pages are already added to LRU */
  if (newly_allocated)
   folio_add_lru(folio);
  folio_add_file_rmap_pte(folio, page, dst_vma);
} else {
  folio_add_new_anon_rmap(folio, dst_vma, dst_addr, RMAP_EXCLUSIVE);
  folio_add_lru_vma(folio, dst_vma);
}

/*
* Must happen after rmap, as mm_counter() checks mapping (via
* PageAnon()), which is set by __page_set_anon_rmap().
*/
inc_mm_counter(dst_mm, mm_counter(folio));

set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
ret = 0;
out_unlock:
pte_unmap_unlock(dst_pte, ptl);
out:
return ret;
}

static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
     struct vm_area_struct *dst_vma,
     unsigned long dst_addr,
     unsigned long src_addr,
     uffd_flags_t flags,
     struct folio **foliop)
{
void *kaddr;
int ret;
struct folio *folio;

if (!*foliop) {
  ret = -ENOMEM;
  folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma,
     dst_addr);
  if (!folio)
   goto out;

  kaddr = kmap_local_folio(folio, 0);
  /*
* The read mmap_lock is held here.  Despite the
* mmap_lock being read recursive a deadlock is still
* possible if a writer has taken a lock.  For example:
*
* process A thread 1 takes read lock on own mmap_lock
* process A thread 2 calls mmap, blocks taking write lock
* process B thread 1 takes page fault, read lock on own mmap lock
* process B thread 2 calls mmap, blocks taking write lock
* process A thread 1 blocks taking read lock on process B
* process B thread 1 blocks taking read lock on process A
*
* Disable page faults to prevent potential deadlock
* and retry the copy outside the mmap_lock.
*/
  pagefault_disable();
  ret = copy_from_user(kaddr, (const void __user *) src_addr,
         PAGE_SIZE);
  pagefault_enable();
  kunmap_local(kaddr);

  /* fallback to copy_from_user outside mmap_lock */
  if (unlikely(ret)) {
   ret = -ENOENT;
   *foliop = folio;
   /* don't free the page */
   goto out;
  }

  flush_dcache_folio(folio);
} else {
  folio = *foliop;
  *foliop = NULL;
}

/*
* The memory barrier inside __folio_mark_uptodate makes sure that
* preceding stores to the page contents become visible before
* the set_pte_at() write.
*/
__folio_mark_uptodate(folio);

ret = -ENOMEM;
if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
  goto out_release;

ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
           &folio->page, true, flags);
if (ret)
  goto out_release;
out:
return ret;
out_release:
folio_put(folio);
goto out;
}

static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd,
      struct vm_area_struct *dst_vma,
      unsigned long dst_addr)
{
struct folio *folio;
int ret = -ENOMEM;

folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr);
if (!folio)
  return ret;

if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
  goto out_put;

/*
* The memory barrier inside __folio_mark_uptodate makes sure that
* zeroing out the folio become visible before mapping the page
* using set_pte_at(). See do_anonymous_page().
*/
__folio_mark_uptodate(folio);

ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
           &folio->page, true, 0);
if (ret)
  goto out_put;

return 0;
out_put:
folio_put(folio);
return ret;
}

static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
         struct vm_area_struct *dst_vma,
         unsigned long dst_addr)
{
pte_t _dst_pte, *dst_pte;
spinlock_t *ptl;
int ret;

if (mm_forbids_zeropage(dst_vma->vm_mm))
  return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);

_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
      dst_vma->vm_page_prot));
ret = -EAGAIN;
dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
if (!dst_pte)
  goto out;
if (mfill_file_over_size(dst_vma, dst_addr)) {
  ret = -EFAULT;
  goto out_unlock;
}
ret = -EEXIST;
if (!pte_none(ptep_get(dst_pte)))
  goto out_unlock;
set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
ret = 0;
out_unlock:
pte_unmap_unlock(dst_pte, ptl);
out:
return ret;
}

/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
static int mfill_atomic_pte_continue(pmd_t *dst_pmd,
         struct vm_area_struct *dst_vma,
         unsigned long dst_addr,
         uffd_flags_t flags)
{
struct inode *inode = file_inode(dst_vma->vm_file);
pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
struct folio *folio;
struct page *page;
int ret;

ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC);
/* Our caller expects us to return -EFAULT if we failed to find folio */
if (ret == -ENOENT)
  ret = -EFAULT;
if (ret)
  goto out;
if (!folio) {
  ret = -EFAULT;
  goto out;
}

page = folio_file_page(folio, pgoff);
if (PageHWPoison(page)) {
  ret = -EIO;
  goto out_release;
}

ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
           page, false, flags);
if (ret)
  goto out_release;

folio_unlock(folio);
ret = 0;
out:
return ret;
out_release:
folio_unlock(folio);
folio_put(folio);
goto out;
}

/* Handles UFFDIO_POISON for all non-hugetlb VMAs. */
static int mfill_atomic_pte_poison(pmd_t *dst_pmd,
       struct vm_area_struct *dst_vma,
       unsigned long dst_addr,
       uffd_flags_t flags)
{
int ret;
struct mm_struct *dst_mm = dst_vma->vm_mm;
pte_t _dst_pte, *dst_pte;
spinlock_t *ptl;

_dst_pte = make_pte_marker(PTE_MARKER_POISONED);
ret = -EAGAIN;
dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
if (!dst_pte)
  goto out;

if (mfill_file_over_size(dst_vma, dst_addr)) {
  ret = -EFAULT;
  goto out_unlock;
}

ret = -EEXIST;
/* Refuse to overwrite any PTE, even a PTE marker (e.g. UFFD WP). */
if (!pte_none(ptep_get(dst_pte)))
  goto out_unlock;

set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

/* No need to invalidate - it was non-present before */
update_mmu_cache(dst_vma, dst_addr, dst_pte);
ret = 0;
out_unlock:
pte_unmap_unlock(dst_pte, ptl);
out:
return ret;
}

static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
{
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;

pgd = pgd_offset(mm, address);
p4d = p4d_alloc(mm, pgd, address);
if (!p4d)
  return NULL;
pud = pud_alloc(mm, p4d, address);
if (!pud)
  return NULL;
/*
* Note that we didn't run this because the pmd was
* missing, the *pmd may be already established and in
* turn it may also be a trans_huge_pmd.
*/
return pmd_alloc(mm, pud, address);
}

#ifdef CONFIG_HUGETLB_PAGE
/*
* mfill_atomic processing for HUGETLB vmas.  Note that this routine is
* called with either vma-lock or mmap_lock held, it will release the lock
* before returning.
*/
static __always_inline ssize_t mfill_atomic_hugetlb(
           struct userfaultfd_ctx *ctx,
           struct vm_area_struct *dst_vma,
           unsigned long dst_start,
           unsigned long src_start,
           unsigned long len,
           uffd_flags_t flags)
{
struct mm_struct *dst_mm = dst_vma->vm_mm;
ssize_t err;
pte_t *dst_pte;
unsigned long src_addr, dst_addr;
long copied;
struct folio *folio;
unsigned long vma_hpagesize;
pgoff_t idx;
u32 hash;
struct address_space *mapping;

/*
* There is no default zero huge page for all huge page sizes as
* supported by hugetlb.  A PMD_SIZE huge pages may exist as used
* by THP.  Since we can not reliably insert a zero page, this
* feature is not supported.
*/
if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
  up_read(&ctx->map_changing_lock);
  uffd_mfill_unlock(dst_vma);
  return -EINVAL;
}

src_addr = src_start;
dst_addr = dst_start;
copied = 0;
folio = NULL;
vma_hpagesize = vma_kernel_pagesize(dst_vma);

/*
* Validate alignment based on huge page size
*/
err = -EINVAL;
if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
  goto out_unlock;

retry:
/*
* On routine entry dst_vma is set.  If we had to drop mmap_lock and
* retry, dst_vma will be set to NULL and we must lookup again.
*/
if (!dst_vma) {
  dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
  if (IS_ERR(dst_vma)) {
   err = PTR_ERR(dst_vma);
   goto out;
  }

  err = -ENOENT;
  if (!is_vm_hugetlb_page(dst_vma))
   goto out_unlock_vma;

  err = -EINVAL;
  if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
   goto out_unlock_vma;

  /*
* If memory mappings are changing because of non-cooperative
* operation (e.g. mremap) running in parallel, bail out and
* request the user to retry later
*/
  down_read(&ctx->map_changing_lock);
  err = -EAGAIN;
  if (atomic_read(&ctx->mmap_changing))
   goto out_unlock;
}

while (src_addr < src_start + len) {
  VM_WARN_ON_ONCE(dst_addr >= dst_start + len);

  /*
* Serialize via vma_lock and hugetlb_fault_mutex.
* vma_lock ensures the dst_pte remains valid even
* in the case of shared pmds.  fault mutex prevents
* races with other faulting threads.
*/
  idx = linear_page_index(dst_vma, dst_addr);
  mapping = dst_vma->vm_file->f_mapping;
  hash = hugetlb_fault_mutex_hash(mapping, idx);
  mutex_lock(&hugetlb_fault_mutex_table[hash]);
  hugetlb_vma_lock_read(dst_vma);

  err = -ENOMEM;
  dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
  if (!dst_pte) {
   hugetlb_vma_unlock_read(dst_vma);
   mutex_unlock(&hugetlb_fault_mutex_table[hash]);
   goto out_unlock;
  }

  if (!uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) &&
      !huge_pte_none_mostly(huge_ptep_get(dst_mm, dst_addr, dst_pte))) {
   err = -EEXIST;
   hugetlb_vma_unlock_read(dst_vma);
   mutex_unlock(&hugetlb_fault_mutex_table[hash]);
   goto out_unlock;
  }

  err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr,
            src_addr, flags, &folio);

  hugetlb_vma_unlock_read(dst_vma);
  mutex_unlock(&hugetlb_fault_mutex_table[hash]);

  cond_resched();

  if (unlikely(err == -ENOENT)) {
   up_read(&ctx->map_changing_lock);
   uffd_mfill_unlock(dst_vma);
   VM_WARN_ON_ONCE(!folio);

   err = copy_folio_from_user(folio,
         (const void __user *)src_addr, true);
   if (unlikely(err)) {
    err = -EFAULT;
    goto out;
   }

   dst_vma = NULL;
   goto retry;
  } else
   VM_WARN_ON_ONCE(folio);

  if (!err) {
   dst_addr += vma_hpagesize;
   src_addr += vma_hpagesize;
   copied += vma_hpagesize;

   if (fatal_signal_pending(current))
    err = -EINTR;
  }
  if (err)
   break;
}

out_unlock:
up_read(&ctx->map_changing_lock);
out_unlock_vma:
uffd_mfill_unlock(dst_vma);
out:
if (folio)
  folio_put(folio);
VM_WARN_ON_ONCE(copied < 0);
VM_WARN_ON_ONCE(err > 0);
VM_WARN_ON_ONCE(!copied && !err);
return copied ? copied : err;
}
#else /* !CONFIG_HUGETLB_PAGE */
/* fail at build time if gcc attempts to use this */
extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
        struct vm_area_struct *dst_vma,
        unsigned long dst_start,
        unsigned long src_start,
        unsigned long len,
        uffd_flags_t flags);
#endif /* CONFIG_HUGETLB_PAGE */

static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd,
      struct vm_area_struct *dst_vma,
      unsigned long dst_addr,
      unsigned long src_addr,
      uffd_flags_t flags,
      struct folio **foliop)
{
ssize_t err;

if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) {
  return mfill_atomic_pte_continue(dst_pmd, dst_vma,
       dst_addr, flags);
} else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
  return mfill_atomic_pte_poison(dst_pmd, dst_vma,
            dst_addr, flags);
}

/*
* The normal page fault path for a shmem will invoke the
* fault, fill the hole in the file and COW it right away. The
* result generates plain anonymous memory. So when we are
* asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll
* generate anonymous memory directly without actually filling
* the hole. For the MAP_PRIVATE case the robustness check
* only happens in the pagetable (to verify it's still none)
* and not in the radix tree.
*/
if (!(dst_vma->vm_flags & VM_SHARED)) {
  if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY))
   err = mfill_atomic_pte_copy(dst_pmd, dst_vma,
          dst_addr, src_addr,
          flags, foliop);
  else
   err = mfill_atomic_pte_zeropage(dst_pmd,
       dst_vma, dst_addr);
} else {
  err = shmem_mfill_atomic_pte(dst_pmd, dst_vma,
          dst_addr, src_addr,
          flags, foliop);
}

return err;
}

static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
         unsigned long dst_start,
         unsigned long src_start,
         unsigned long len,
         uffd_flags_t flags)
{
struct mm_struct *dst_mm = ctx->mm;
struct vm_area_struct *dst_vma;
ssize_t err;
pmd_t *dst_pmd;
unsigned long src_addr, dst_addr;
long copied;
struct folio *folio;

/*
* Sanitize the command parameters:
*/
VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
VM_WARN_ON_ONCE(len & ~PAGE_MASK);

/* Does the address range wrap, or is the span zero-sized? */
VM_WARN_ON_ONCE(src_start + len <= src_start);
VM_WARN_ON_ONCE(dst_start + len <= dst_start);

src_addr = src_start;
dst_addr = dst_start;
copied = 0;
folio = NULL;
retry:
/*
* Make sure the vma is not shared, that the dst range is
* both valid and fully within a single existing vma.
*/
dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
if (IS_ERR(dst_vma)) {
  err = PTR_ERR(dst_vma);
  goto out;
}

/*
* If memory mappings are changing because of non-cooperative
* operation (e.g. mremap) running in parallel, bail out and
* request the user to retry later
*/
down_read(&ctx->map_changing_lock);
err = -EAGAIN;
if (atomic_read(&ctx->mmap_changing))
  goto out_unlock;

err = -EINVAL;
/*
* shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
* it will overwrite vm_ops, so vma_is_anonymous must return false.
*/
if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
     dst_vma->vm_flags & VM_SHARED))
  goto out_unlock;

/*
* validate 'mode' now that we know the dst_vma: don't allow
* a wrprotect copy if the userfaultfd didn't register as WP.
*/
if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP))
  goto out_unlock;

/*
* If this is a HUGETLB vma, pass off to appropriate routine
*/
if (is_vm_hugetlb_page(dst_vma))
  return  mfill_atomic_hugetlb(ctx, dst_vma, dst_start,
          src_start, len, flags);

if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
  goto out_unlock;
if (!vma_is_shmem(dst_vma) &&
     uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
  goto out_unlock;

while (src_addr < src_start + len) {
  pmd_t dst_pmdval;

  VM_WARN_ON_ONCE(dst_addr >= dst_start + len);

  dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
  if (unlikely(!dst_pmd)) {
   err = -ENOMEM;
   break;
  }

  dst_pmdval = pmdp_get_lockless(dst_pmd);
  if (unlikely(pmd_none(dst_pmdval)) &&
      unlikely(__pte_alloc(dst_mm, dst_pmd))) {
   err = -ENOMEM;
   break;
  }
  dst_pmdval = pmdp_get_lockless(dst_pmd);
  /*
* If the dst_pmd is THP don't override it and just be strict.
* (This includes the case where the PMD used to be THP and
* changed back to none after __pte_alloc().)
*/
  if (unlikely(!pmd_present(dst_pmdval) ||
    pmd_trans_huge(dst_pmdval))) {
   err = -EEXIST;
   break;
  }
  if (unlikely(pmd_bad(dst_pmdval))) {
   err = -EFAULT;
   break;
  }
  /*
* For shmem mappings, khugepaged is allowed to remove page
* tables under us; pte_offset_map_lock() will deal with that.
*/

  err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr,
           src_addr, flags, &folio);
  cond_resched();

  if (unlikely(err == -ENOENT)) {
   void *kaddr;

   up_read(&ctx->map_changing_lock);
   uffd_mfill_unlock(dst_vma);
   VM_WARN_ON_ONCE(!folio);

   kaddr = kmap_local_folio(folio, 0);
   err = copy_from_user(kaddr,
          (const void __user *) src_addr,
          PAGE_SIZE);
   kunmap_local(kaddr);
   if (unlikely(err)) {
    err = -EFAULT;
    goto out;
   }
   flush_dcache_folio(folio);
   goto retry;
  } else
   VM_WARN_ON_ONCE(folio);

  if (!err) {
   dst_addr += PAGE_SIZE;
   src_addr += PAGE_SIZE;
   copied += PAGE_SIZE;

   if (fatal_signal_pending(current))
    err = -EINTR;
  }
  if (err)
   break;
}

out_unlock:
up_read(&ctx->map_changing_lock);
uffd_mfill_unlock(dst_vma);
out:
if (folio)
  folio_put(folio);
VM_WARN_ON_ONCE(copied < 0);
VM_WARN_ON_ONCE(err > 0);
VM_WARN_ON_ONCE(!copied && !err);
return copied ? copied : err;
}

ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
     unsigned long src_start, unsigned long len,
     uffd_flags_t flags)
{
return mfill_atomic(ctx, dst_start, src_start, len,
       uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));
}

ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,
         unsigned long start,
         unsigned long len)
{
return mfill_atomic(ctx, start, 0, len,
       uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));
}

ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,
         unsigned long len, uffd_flags_t flags)
{

/*
* A caller might reasonably assume that UFFDIO_CONTINUE contains an
* smp_wmb() to ensure that any writes to the about-to-be-mapped page by
* the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to
* subsequent loads from the page through the newly mapped address range.
*/
smp_wmb();

return mfill_atomic(ctx, start, 0, len,
       uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));
}

ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,
       unsigned long len, uffd_flags_t flags)
{
return mfill_atomic(ctx, start, 0, len,
       uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));
}

long uffd_wp_range(struct vm_area_struct *dst_vma,
     unsigned long start, unsigned long len, bool enable_wp)
{
unsigned int mm_cp_flags;
struct mmu_gather tlb;
long ret;

VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end,
   "The address range exceeds VMA boundary.\n");
if (enable_wp)
  mm_cp_flags = MM_CP_UFFD_WP;
else
  mm_cp_flags = MM_CP_UFFD_WP_RESOLVE;

/*
* vma->vm_page_prot already reflects that uffd-wp is enabled for this
* VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed
* to be write-protected as default whenever protection changes.
* Try upgrading write permissions manually.
*/
if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma))
  mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
tlb_gather_mmu(&tlb, dst_vma->vm_mm);
ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags);
tlb_finish_mmu(&tlb);

return ret;
}

int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
   unsigned long len, bool enable_wp)
{
struct mm_struct *dst_mm = ctx->mm;
unsigned long end = start + len;
unsigned long _start, _end;
struct vm_area_struct *dst_vma;
unsigned long page_mask;
long err;
VMA_ITERATOR(vmi, dst_mm, start);

/*
* Sanitize the command parameters:
*/
VM_WARN_ON_ONCE(start & ~PAGE_MASK);
VM_WARN_ON_ONCE(len & ~PAGE_MASK);

/* Does the address range wrap, or is the span zero-sized? */
VM_WARN_ON_ONCE(start + len <= start);

mmap_read_lock(dst_mm);

/*
* If memory mappings are changing because of non-cooperative
* operation (e.g. mremap) running in parallel, bail out and
* request the user to retry later
*/
down_read(&ctx->map_changing_lock);
err = -EAGAIN;
if (atomic_read(&ctx->mmap_changing))
  goto out_unlock;

err = -ENOENT;
for_each_vma_range(vmi, dst_vma, end) {

  if (!userfaultfd_wp(dst_vma)) {
   err = -ENOENT;
   break;
  }

  if (is_vm_hugetlb_page(dst_vma)) {
   err = -EINVAL;
   page_mask = vma_kernel_pagesize(dst_vma) - 1;
   if ((start & page_mask) || (len & page_mask))
    break;
  }

  _start = max(dst_vma->vm_start, start);
  _end = min(dst_vma->vm_end, end);

  err = uffd_wp_range(dst_vma, _start, _end - _start, enable_wp);

  /* Return 0 on success, <0 on failures */
  if (err < 0)
   break;
  err = 0;
}
out_unlock:
up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
return err;
}

void double_pt_lock(spinlock_t *ptl1,
      spinlock_t *ptl2)
__acquires(ptl1)
__acquires(ptl2)
{
if (ptl1 > ptl2)
  swap(ptl1, ptl2);
/* lock in virtual address order to avoid lock inversion */
spin_lock(ptl1);
if (ptl1 != ptl2)
  spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING);
else
  __acquire(ptl2);
}

void double_pt_unlock(spinlock_t *ptl1,
        spinlock_t *ptl2)
__releases(ptl1)
__releases(ptl2)
{
spin_unlock(ptl1);
if (ptl1 != ptl2)
  spin_unlock(ptl2);
else
  __release(ptl2);
}

static inline bool is_pte_pages_stable(pte_t *dst_pte, pte_t *src_pte,
           pte_t orig_dst_pte, pte_t orig_src_pte,
           pmd_t *dst_pmd, pmd_t dst_pmdval)
{
return pte_same(ptep_get(src_pte), orig_src_pte) &&
        pte_same(ptep_get(dst_pte), orig_dst_pte) &&
        pmd_same(dst_pmdval, pmdp_get_lockless(dst_pmd));
}

static int move_present_pte(struct mm_struct *mm,
       struct vm_area_struct *dst_vma,
       struct vm_area_struct *src_vma,
       unsigned long dst_addr, unsigned long src_addr,
       pte_t *dst_pte, pte_t *src_pte,
       pte_t orig_dst_pte, pte_t orig_src_pte,
       pmd_t *dst_pmd, pmd_t dst_pmdval,
       spinlock_t *dst_ptl, spinlock_t *src_ptl,
       struct folio *src_folio)
{
int err = 0;

double_pt_lock(dst_ptl, src_ptl);

if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
     dst_pmd, dst_pmdval)) {
  err = -EAGAIN;
  goto out;
}
if (folio_test_large(src_folio) ||
     folio_maybe_dma_pinned(src_folio) ||
     !PageAnonExclusive(&src_folio->page)) {
  err = -EBUSY;
  goto out;
}

orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
/* Folio got pinned from under us. Put it back and fail the move. */
if (folio_maybe_dma_pinned(src_folio)) {
  set_pte_at(mm, src_addr, src_pte, orig_src_pte);
  err = -EBUSY;
  goto out;
}

folio_move_anon_rmap(src_folio, dst_vma);
src_folio->index = linear_page_index(dst_vma, dst_addr);

orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
/* Set soft dirty bit so userspace can notice the pte was moved */
#ifdef CONFIG_MEM_SOFT_DIRTY
orig_dst_pte = pte_mksoft_dirty(orig_dst_pte);
#endif
if (pte_dirty(orig_src_pte))
  orig_dst_pte = pte_mkdirty(orig_dst_pte);
orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma);

set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte);
out:
double_pt_unlock(dst_ptl, src_ptl);
return err;
}

static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
    unsigned long dst_addr, unsigned long src_addr,
    pte_t *dst_pte, pte_t *src_pte,
    pte_t orig_dst_pte, pte_t orig_src_pte,
    pmd_t *dst_pmd, pmd_t dst_pmdval,
    spinlock_t *dst_ptl, spinlock_t *src_ptl,
    struct folio *src_folio,
    struct swap_info_struct *si, swp_entry_t entry)
{
/*
* Check if the folio still belongs to the target swap entry after
* acquiring the lock. Folio can be freed in the swap cache while
* not locked.
*/
if (src_folio && unlikely(!folio_test_swapcache(src_folio) ||
      entry.val != src_folio->swap.val))
  return -EAGAIN;

double_pt_lock(dst_ptl, src_ptl);

if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
     dst_pmd, dst_pmdval)) {
  double_pt_unlock(dst_ptl, src_ptl);
  return -EAGAIN;
}

/*
* The src_folio resides in the swapcache, requiring an update to its
* index and mapping to align with the dst_vma, where a swap-in may
* occur and hit the swapcache after moving the PTE.
*/
if (src_folio) {
  folio_move_anon_rmap(src_folio, dst_vma);
  src_folio->index = linear_page_index(dst_vma, dst_addr);
} else {
  /*
* Check if the swap entry is cached after acquiring the src_pte
* lock. Otherwise, we might miss a newly loaded swap cache folio.
*
* Check swap_map directly to minimize overhead, READ_ONCE is sufficient.
* We are trying to catch newly added swap cache, the only possible case is
* when a folio is swapped in and out again staying in swap cache, using the
* same entry before the PTE check above. The PTL is acquired and released
* twice, each time after updating the swap_map's flag. So holding
* the PTL here ensures we see the updated value. False positive is possible,
* e.g. SWP_SYNCHRONOUS_IO swapin may set the flag without touching the
* cache, or during the tiny synchronization window between swap cache and
* swap_map, but it will be gone very quickly, worst result is retry jitters.
*/
  if (READ_ONCE(si->swap_map[swp_offset(entry)]) & SWAP_HAS_CACHE) {
   double_pt_unlock(dst_ptl, src_ptl);
   return -EAGAIN;
  }
}

orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
#ifdef CONFIG_MEM_SOFT_DIRTY
orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte);
#endif
set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
double_pt_unlock(dst_ptl, src_ptl);

return 0;
}

static int move_zeropage_pte(struct mm_struct *mm,
        struct vm_area_struct *dst_vma,
        struct vm_area_struct *src_vma,
        unsigned long dst_addr, unsigned long src_addr,
        pte_t *dst_pte, pte_t *src_pte,
        pte_t orig_dst_pte, pte_t orig_src_pte,
        pmd_t *dst_pmd, pmd_t dst_pmdval,
        spinlock_t *dst_ptl, spinlock_t *src_ptl)
{
pte_t zero_pte;

double_pt_lock(dst_ptl, src_ptl);
if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
     dst_pmd, dst_pmdval)) {
  double_pt_unlock(dst_ptl, src_ptl);
  return -EAGAIN;
}

zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
      dst_vma->vm_page_prot));
ptep_clear_flush(src_vma, src_addr, src_pte);
set_pte_at(mm, dst_addr, dst_pte, zero_pte);
double_pt_unlock(dst_ptl, src_ptl);

return 0;
}

/*
* The mmap_lock for reading is held by the caller. Just move the page
* from src_pmd to dst_pmd if possible, and return true if succeeded
* in moving the page.
*/
static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
     struct vm_area_struct *dst_vma,
     struct vm_area_struct *src_vma,
     unsigned long dst_addr, unsigned long src_addr,
     __u64 mode)
{
swp_entry_t entry;
struct swap_info_struct *si = NULL;
pte_t orig_src_pte, orig_dst_pte;
pte_t src_folio_pte;
spinlock_t *src_ptl, *dst_ptl;
pte_t *src_pte = NULL;
pte_t *dst_pte = NULL;
pmd_t dummy_pmdval;
pmd_t dst_pmdval;
struct folio *src_folio = NULL;
struct anon_vma *src_anon_vma = NULL;
struct mmu_notifier_range range;
int err = 0;

flush_cache_range(src_vma, src_addr, src_addr + PAGE_SIZE);
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
    src_addr, src_addr + PAGE_SIZE);
mmu_notifier_invalidate_range_start(&range);
retry:
/*
* Use the maywrite version to indicate that dst_pte will be modified,
* since dst_pte needs to be none, the subsequent pte_same() check
* cannot prevent the dst_pte page from being freed concurrently, so we
* also need to abtain dst_pmdval and recheck pmd_same() later.
*/
dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dst_pmdval,
        &dst_ptl);

/* Retry if a huge pmd materialized from under us */
if (unlikely(!dst_pte)) {
  err = -EAGAIN;
  goto out;
}

/*
* Unlike dst_pte, the subsequent pte_same() check can ensure the
* stability of the src_pte page, so there is no need to get pmdval,
* just pass a dummy variable to it.
*/
src_pte = pte_offset_map_rw_nolock(mm, src_pmd, src_addr, &dummy_pmdval,
        &src_ptl);

/*
* We held the mmap_lock for reading so MADV_DONTNEED
* can zap transparent huge pages under us, or the
* transparent huge page fault can establish new
* transparent huge pages under us.
*/
if (unlikely(!src_pte)) {
  err = -EAGAIN;
  goto out;
}

/* Sanity checks before the operation */
if (pmd_none(*dst_pmd) || pmd_none(*src_pmd) ||
     pmd_trans_huge(*dst_pmd) || pmd_trans_huge(*src_pmd)) {
  err = -EINVAL;
  goto out;
}

spin_lock(dst_ptl);
orig_dst_pte = ptep_get(dst_pte);
spin_unlock(dst_ptl);
if (!pte_none(orig_dst_pte)) {
  err = -EEXIST;
  goto out;
}

spin_lock(src_ptl);
orig_src_pte = ptep_get(src_pte);
spin_unlock(src_ptl);
if (pte_none(orig_src_pte)) {
  if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES))
   err = -ENOENT;
  else /* nothing to do to move a hole */
   err = 0;
  goto out;
}

/* If PTE changed after we locked the folio them start over */
if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) {
  err = -EAGAIN;
  goto out;
}

if (pte_present(orig_src_pte)) {
  if (is_zero_pfn(pte_pfn(orig_src_pte))) {
   err = move_zeropage_pte(mm, dst_vma, src_vma,
            dst_addr, src_addr, dst_pte, src_pte,
            orig_dst_pte, orig_src_pte,
            dst_pmd, dst_pmdval, dst_ptl, src_ptl);
   goto out;
  }

  /*
* Pin and lock both source folio and anon_vma. Since we are in
* RCU read section, we can't block, so on contention have to
* unmap the ptes, obtain the lock and retry.
*/
  if (!src_folio) {
   struct folio *folio;
   bool locked;

   /*
* Pin the page while holding the lock to be sure the
* page isn't freed under us
*/
   spin_lock(src_ptl);
   if (!pte_same(orig_src_pte, ptep_get(src_pte))) {
    spin_unlock(src_ptl);
    err = -EAGAIN;
    goto out;
   }

   folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
   if (!folio || !PageAnonExclusive(&folio->page)) {
    spin_unlock(src_ptl);
    err = -EBUSY;
    goto out;
   }

   locked = folio_trylock(folio);
   /*
* We avoid waiting for folio lock with a raised
* refcount for large folios because extra refcounts
* will result in split_folio() failing later and
* retrying.  If multiple tasks are trying to move a
* large folio we can end up livelocking.
*/
   if (!locked && folio_test_large(folio)) {
    spin_unlock(src_ptl);
    err = -EAGAIN;
    goto out;
   }

   folio_get(folio);
   src_folio = folio;
   src_folio_pte = orig_src_pte;
   spin_unlock(src_ptl);

   if (!locked) {
    pte_unmap(src_pte);
    pte_unmap(dst_pte);
    src_pte = dst_pte = NULL;
    /* now we can block and wait */
    folio_lock(src_folio);
    goto retry;
   }

   if (WARN_ON_ONCE(!folio_test_anon(src_folio))) {
    err = -EBUSY;
    goto out;
   }
  }

  /* at this point we have src_folio locked */
  if (folio_test_large(src_folio)) {
   /* split_folio() can block */
   pte_unmap(src_pte);
   pte_unmap(dst_pte);
   src_pte = dst_pte = NULL;
   err = split_folio(src_folio);
   if (err)
    goto out;
   /* have to reacquire the folio after it got split */
   folio_unlock(src_folio);
   folio_put(src_folio);
   src_folio = NULL;
   goto retry;
  }

  if (!src_anon_vma) {
   /*
* folio_referenced walks the anon_vma chain
* without the folio lock. Serialize against it with
* the anon_vma lock, the folio lock is not enough.
*/
   src_anon_vma = folio_get_anon_vma(src_folio);
   if (!src_anon_vma) {
    /* page was unmapped from under us */
    err = -EAGAIN;
    goto out;
   }
   if (!anon_vma_trylock_write(src_anon_vma)) {
    pte_unmap(src_pte);
    pte_unmap(dst_pte);
    src_pte = dst_pte = NULL;
    /* now we can block and wait */
    anon_vma_lock_write(src_anon_vma);
    goto retry;
   }
  }

  err = move_present_pte(mm,  dst_vma, src_vma,
           dst_addr, src_addr, dst_pte, src_pte,
           orig_dst_pte, orig_src_pte, dst_pmd,
           dst_pmdval, dst_ptl, src_ptl, src_folio);
} else {
  struct folio *folio = NULL;

  entry = pte_to_swp_entry(orig_src_pte);
  if (non_swap_entry(entry)) {
   if (is_migration_entry(entry)) {
    pte_unmap(src_pte);
    pte_unmap(dst_pte);
    src_pte = dst_pte = NULL;
    migration_entry_wait(mm, src_pmd, src_addr);
    err = -EAGAIN;
   } else
    err = -EFAULT;
   goto out;
  }

  if (!pte_swp_exclusive(orig_src_pte)) {
   err = -EBUSY;
   goto out;
  }

  si = get_swap_device(entry);
  if (unlikely(!si)) {
   err = -EAGAIN;
   goto out;
  }
  /*
* Verify the existence of the swapcache. If present, the folio's
* index and mapping must be updated even when the PTE is a swap
* entry. The anon_vma lock is not taken during this process since
* the folio has already been unmapped, and the swap entry is
* exclusive, preventing rmap walks.
*
* For large folios, return -EBUSY immediately, as split_folio()
* also returns -EBUSY when attempting to split unmapped large
* folios in the swapcache. This issue needs to be resolved
* separately to allow proper handling.
*/
  if (!src_folio)
   folio = filemap_get_folio(swap_address_space(entry),
     swap_cache_index(entry));
  if (!IS_ERR_OR_NULL(folio)) {
   if (folio_test_large(folio)) {
    err = -EBUSY;
    folio_put(folio);
    goto out;
   }
   src_folio = folio;
   src_folio_pte = orig_src_pte;
   if (!folio_trylock(src_folio)) {
    pte_unmap(src_pte);
    pte_unmap(dst_pte);
    src_pte = dst_pte = NULL;
    put_swap_device(si);
    si = NULL;
    /* now we can block and wait */
    folio_lock(src_folio);
    goto retry;
   }
  }
  err = move_swap_pte(mm, dst_vma, dst_addr, src_addr, dst_pte, src_pte,
    orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval,
    dst_ptl, src_ptl, src_folio, si, entry);
}

out:
if (src_anon_vma) {
  anon_vma_unlock_write(src_anon_vma);
  put_anon_vma(src_anon_vma);
}
if (src_folio) {
  folio_unlock(src_folio);
  folio_put(src_folio);
}
/*
* Unmap in reverse order (LIFO) to maintain proper kmap_local
* index ordering when CONFIG_HIGHPTE is enabled. We mapped dst_pte
* first, then src_pte, so we must unmap src_pte first, then dst_pte.
*/
if (src_pte)
  pte_unmap(src_pte);
if (dst_pte)
  pte_unmap(dst_pte);
mmu_notifier_invalidate_range_end(&range);
if (si)
  put_swap_device(si);

return err;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline bool move_splits_huge_pmd(unsigned long dst_addr,
     unsigned long src_addr,
     unsigned long src_end)
{
return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) ||
  src_end - src_addr < HPAGE_PMD_SIZE;
}
#else
static inline bool move_splits_huge_pmd(unsigned long dst_addr,
     unsigned long src_addr,
     unsigned long src_end)
{
/* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */
return false;
}
#endif

static inline bool vma_move_compatible(struct vm_area_struct *vma)
{
return !(vma->vm_flags & (VM_PFNMAP | VM_IO |  VM_HUGETLB |
      VM_MIXEDMAP | VM_SHADOW_STACK));
}

static int validate_move_areas(struct userfaultfd_ctx *ctx,
          struct vm_area_struct *src_vma,
          struct vm_area_struct *dst_vma)
{
/* Only allow moving if both have the same access and protection */
if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) ||
     pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot))
  return -EINVAL;

/* Only allow moving if both are mlocked or both aren't */
if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED))
  return -EINVAL;

/*
* For now, we keep it simple and only move between writable VMAs.
* Access flags are equal, therefore cheching only the source is enough.
*/
if (!(src_vma->vm_flags & VM_WRITE))
  return -EINVAL;

/* Check if vma flags indicate content which can be moved */
if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma))
  return -EINVAL;

/* Ensure dst_vma is registered in uffd we are operating on */
if (!dst_vma->vm_userfaultfd_ctx.ctx ||
     dst_vma->vm_userfaultfd_ctx.ctx != ctx)
  return -EINVAL;

/* Only allow moving across anonymous vmas */
if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
  return -EINVAL;

return 0;
}

static __always_inline
int find_vmas_mm_locked(struct mm_struct *mm,
   unsigned long dst_start,
   unsigned long src_start,
   struct vm_area_struct **dst_vmap,
   struct vm_area_struct **src_vmap)
{
struct vm_area_struct *vma;

mmap_assert_locked(mm);
vma = find_vma_and_prepare_anon(mm, dst_start);
if (IS_ERR(vma))
  return PTR_ERR(vma);

*dst_vmap = vma;
/* Skip finding src_vma if src_start is in dst_vma */
if (src_start >= vma->vm_start && src_start < vma->vm_end)
  goto out_success;

vma = vma_lookup(mm, src_start);
if (!vma)
  return -ENOENT;
out_success:
*src_vmap = vma;
return 0;
}

#ifdef CONFIG_PER_VMA_LOCK
static int uffd_move_lock(struct mm_struct *mm,
     unsigned long dst_start,
     unsigned long src_start,
     struct vm_area_struct **dst_vmap,
     struct vm_area_struct **src_vmap)
{
struct vm_area_struct *vma;
int err;

vma = uffd_lock_vma(mm, dst_start);
if (IS_ERR(vma))
  return PTR_ERR(vma);

*dst_vmap = vma;
/*
* Skip finding src_vma if src_start is in dst_vma. This also ensures
* that we don't lock the same vma twice.
*/
if (src_start >= vma->vm_start && src_start < vma->vm_end) {
  *src_vmap = vma;
  return 0;
}

/*
* Using uffd_lock_vma() to get src_vma can lead to following deadlock:
*
* Thread1 Thread2
* ------- -------
* vma_start_read(dst_vma)
* mmap_write_lock(mm)
* vma_start_write(src_vma)
* vma_start_read(src_vma)
* mmap_read_lock(mm)
* vma_start_write(dst_vma)
*/
*src_vmap = lock_vma_under_rcu(mm, src_start);
if (likely(*src_vmap))
  return 0;

/* Undo any locking and retry in mmap_lock critical section */
vma_end_read(*dst_vmap);

mmap_read_lock(mm);
err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
if (err)
  goto out;

if (!vma_start_read_locked(*dst_vmap)) {
  err = -EAGAIN;
  goto out;
}

/* Nothing further to do if both vmas are locked. */
if (*dst_vmap == *src_vmap)
  goto out;

if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) {
  /* Undo dst_vmap locking if src_vmap failed to lock */
  vma_end_read(*dst_vmap);
  err = -EAGAIN;
}
out:
mmap_read_unlock(mm);
return err;
}

static void uffd_move_unlock(struct vm_area_struct *dst_vma,
        struct vm_area_struct *src_vma)
{
vma_end_read(src_vma);
if (src_vma != dst_vma)
  vma_end_read(dst_vma);
}

#else

static int uffd_move_lock(struct mm_struct *mm,
     unsigned long dst_start,
     unsigned long src_start,
     struct vm_area_struct **dst_vmap,
     struct vm_area_struct **src_vmap)
{
int err;

mmap_read_lock(mm);
err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
if (err)
  mmap_read_unlock(mm);
return err;
}

static void uffd_move_unlock(struct vm_area_struct *dst_vma,
        struct vm_area_struct *src_vma)
{
mmap_assert_locked(src_vma->vm_mm);
mmap_read_unlock(dst_vma->vm_mm);
}
#endif

/**
* move_pages - move arbitrary anonymous pages of an existing vma
* @ctx: pointer to the userfaultfd context
* @dst_start: start of the destination virtual memory range
* @src_start: start of the source virtual memory range
* @len: length of the virtual memory range
* @mode: flags from uffdio_move.mode
*
* It will either use the mmap_lock in read mode or per-vma locks
*
* move_pages() remaps arbitrary anonymous pages atomically in zero
* copy. It only works on non shared anonymous pages because those can
* be relocated without generating non linear anon_vmas in the rmap
* code.
*
* It provides a zero copy mechanism to handle userspace page faults.
* The source vma pages should have mapcount == 1, which can be
* enforced by using madvise(MADV_DONTFORK) on src vma.
*
* The thread receiving the page during the userland page fault
* will receive the faulting page in the source vma through the network,
* storage or any other I/O device (MADV_DONTFORK in the source vma
* avoids move_pages() to fail with -EBUSY if the process forks before
* move_pages() is called), then it will call move_pages() to map the
* page in the faulting address in the destination vma.
*
* This userfaultfd command works purely via pagetables, so it's the
* most efficient way to move physical non shared anonymous pages
* across different virtual addresses. Unlike mremap()/mmap()/munmap()
* it does not create any new vmas. The mapping in the destination
* address is atomic.
*
* It only works if the vma protection bits are identical from the
* source and destination vma.
*
* It can remap non shared anonymous pages within the same vma too.
*
* If the source virtual memory range has any unmapped holes, or if
* the destination virtual memory range is not a whole unmapped hole,
* move_pages() will fail respectively with -ENOENT or -EEXIST. This
* provides a very strict behavior to avoid any chance of memory
* corruption going unnoticed if there are userland race conditions.
* Only one thread should resolve the userland page fault at any given
* time for any given faulting address. This means that if two threads
* try to both call move_pages() on the same destination address at the
* same time, the second thread will get an explicit error from this
* command.
*
* The command retval will return "len" is successful. The command
* however can be interrupted by fatal signals or errors. If
* interrupted it will return the number of bytes successfully
* remapped before the interruption if any, or the negative error if
* none. It will never return zero. Either it will return an error or
* an amount of bytes successfully moved. If the retval reports a
* "short" remap, the move_pages() command should be repeated by
* userland with src+retval, dst+reval, len-retval if it wants to know
* about the error that interrupted it.
*
* The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to
* prevent -ENOENT errors to materialize if there are holes in the
* source virtual range that is being remapped. The holes will be
* accounted as successfully remapped in the retval of the
* command. This is mostly useful to remap hugepage naturally aligned
* virtual regions without knowing if there are transparent hugepage
* in the regions or not, but preventing the risk of having to split
* the hugepmd during the remap.
*
* If there's any rmap walk that is taking the anon_vma locks without
* first obtaining the folio lock (the only current instance is
* folio_referenced), they will have to verify if the folio->mapping
* has changed after taking the anon_vma lock. If it changed they
* should release the lock and retry obtaining a new anon_vma, because
* it means the anon_vma was changed by move_pages() before the lock
* could be obtained. This is the only additional complexity added to
* the rmap code to provide this anonymous page remapping functionality.
*/
ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
     unsigned long src_start, unsigned long len, __u64 mode)
{
struct mm_struct *mm = ctx->mm;
struct vm_area_struct *src_vma, *dst_vma;
unsigned long src_addr, dst_addr;
pmd_t *src_pmd, *dst_pmd;
long err = -EINVAL;
ssize_t moved = 0;

/* Sanitize the command parameters. */
VM_WARN_ON_ONCE(src_start & ~PAGE_MASK);
VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
VM_WARN_ON_ONCE(len & ~PAGE_MASK);

/* Does the address range wrap, or is the span zero-sized? */
VM_WARN_ON_ONCE(src_start + len < src_start);
VM_WARN_ON_ONCE(dst_start + len < dst_start);

err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
if (err)
  goto out;

/* Re-check after taking map_changing_lock */
err = -EAGAIN;
down_read(&ctx->map_changing_lock);
if (likely(atomic_read(&ctx->mmap_changing)))
  goto out_unlock;
/*
* Make sure the vma is not shared, that the src and dst remap
* ranges are both valid and fully within a single existing
* vma.
*/
err = -EINVAL;
if (src_vma->vm_flags & VM_SHARED)
  goto out_unlock;
if (src_start + len > src_vma->vm_end)
  goto out_unlock;

if (dst_vma->vm_flags & VM_SHARED)
  goto out_unlock;
if (dst_start + len > dst_vma->vm_end)
  goto out_unlock;

err = validate_move_areas(ctx, src_vma, dst_vma);
if (err)
  goto out_unlock;

for (src_addr = src_start, dst_addr = dst_start;
      src_addr < src_start + len;) {
  spinlock_t *ptl;
  pmd_t dst_pmdval;
  unsigned long step_size;

  /*
* Below works because anonymous area would not have a
* transparent huge PUD. If file-backed support is added,
* that case would need to be handled here.
*/
  src_pmd = mm_find_pmd(mm, src_addr);
  if (unlikely(!src_pmd)) {
   if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
    err = -ENOENT;
    break;
   }
   src_pmd = mm_alloc_pmd(mm, src_addr);
   if (unlikely(!src_pmd)) {
    err = -ENOMEM;
    break;
   }
  }
  dst_pmd = mm_alloc_pmd(mm, dst_addr);
  if (unlikely(!dst_pmd)) {
   err = -ENOMEM;
   break;
  }

  dst_pmdval = pmdp_get_lockless(dst_pmd);
  /*
* If the dst_pmd is mapped as THP don't override it and just
* be strict. If dst_pmd changes into TPH after this check, the
* move_pages_huge_pmd() will detect the change and retry
* while move_pages_pte() will detect the change and fail.
*/
  if (unlikely(pmd_trans_huge(dst_pmdval))) {
   err = -EEXIST;
   break;
  }

  ptl = pmd_trans_huge_lock(src_pmd, src_vma);
  if (ptl) {
   /* Check if we can move the pmd without splitting it. */
   if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
       !pmd_none(dst_pmdval)) {
    /* Can be a migration entry */
    if (pmd_present(*src_pmd)) {
     struct folio *folio = pmd_folio(*src_pmd);

     if (!is_huge_zero_folio(folio) &&
         !PageAnonExclusive(&folio->page)) {
      spin_unlock(ptl);
      err = -EBUSY;
      break;
     }
    }

    spin_unlock(ptl);
    split_huge_pmd(src_vma, src_pmd, src_addr);
    /* The folio will be split by move_pages_pte() */
    continue;
   }

   err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
        dst_pmdval, dst_vma, src_vma,
        dst_addr, src_addr);
   step_size = HPAGE_PMD_SIZE;
  } else {
   if (pmd_none(*src_pmd)) {
    if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
     err = -ENOENT;
     break;
    }
    if (unlikely(__pte_alloc(mm, src_pmd))) {
     err = -ENOMEM;
     break;
    }
   }

   if (unlikely(pte_alloc(mm, dst_pmd))) {
    err = -ENOMEM;
    break;
   }

   err = move_pages_pte(mm, dst_pmd, src_pmd,
          dst_vma, src_vma,
          dst_addr, src_addr, mode);
   step_size = PAGE_SIZE;
  }

  cond_resched();

  if (fatal_signal_pending(current)) {
   /* Do not override an error */
   if (!err || err == -EAGAIN)
    err = -EINTR;
   break;
  }

  if (err) {
   if (err == -EAGAIN)
    continue;
   break;
  }

  /* Proceed to the next page */
  dst_addr += step_size;
  src_addr += step_size;
  moved += step_size;
}

out_unlock:
up_read(&ctx->map_changing_lock);
uffd_move_unlock(dst_vma, src_vma);
out:
VM_WARN_ON_ONCE(moved < 0);
VM_WARN_ON_ONCE(err > 0);
VM_WARN_ON_ONCE(!moved && !err);
return moved ? moved : err;
}

static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
         vm_flags_t vm_flags)
{
const bool uffd_wp_changed = (vma->vm_flags ^ vm_flags) & VM_UFFD_WP;

vm_flags_reset(vma, vm_flags);
/*
* For shared mappings, we want to enable writenotify while
* userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
* recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
*/
if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
  vma_set_page_prot(vma);
}

static void userfaultfd_set_ctx(struct vm_area_struct *vma,
    struct userfaultfd_ctx *ctx,
    vm_flags_t vm_flags)
{
vma_start_write(vma);
vma->vm_userfaultfd_ctx = (struct vm_userfaultfd_ctx){ctx};
userfaultfd_set_vm_flags(vma,
     (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags);
}

void userfaultfd_reset_ctx(struct vm_area_struct *vma)
{
userfaultfd_set_ctx(vma, NULL, 0);
}

struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
          struct vm_area_struct *prev,
          struct vm_area_struct *vma,
          unsigned long start,
          unsigned long end)
{
struct vm_area_struct *ret;
bool give_up_on_oom = false;

/*
* If we are modifying only and not splitting, just give up on the merge
* if OOM prevents us from merging successfully.
*/
if (start == vma->vm_start && end == vma->vm_end)
  give_up_on_oom = true;

/* Reset ptes for the whole vma range if wr-protected */
if (userfaultfd_wp(vma))
  uffd_wp_range(vma, start, end - start, false);

ret = vma_modify_flags_uffd(vmi, prev, vma, start, end,
        vma->vm_flags & ~__VM_UFFD_FLAGS,
        NULL_VM_UFFD_CTX, give_up_on_oom);

/*
* In the vma_merge() successful mprotect-like case 8:
* the next vma was merged into the current one and
* the current one has not been updated yet.
*/
if (!IS_ERR(ret))
  userfaultfd_reset_ctx(ret);

return ret;
}

/* Assumes mmap write lock taken, and mm_struct pinned. */
int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
          struct vm_area_struct *vma,
          vm_flags_t vm_flags,
          unsigned long start, unsigned long end,
          bool wp_async)
{
VMA_ITERATOR(vmi, ctx->mm, start);
struct vm_area_struct *prev = vma_prev(&vmi);
unsigned long vma_end;
vm_flags_t new_flags;

if (vma->vm_start < start)
  prev = vma;

for_each_vma_range(vmi, vma, end) {
  cond_resched();

  VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async));
  VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx &&
    vma->vm_userfaultfd_ctx.ctx != ctx);
  VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));

  /*
* Nothing to do: this vma is already registered into this
* userfaultfd and with the right tracking mode too.
*/
  if (vma->vm_userfaultfd_ctx.ctx == ctx &&
      (vma->vm_flags & vm_flags) == vm_flags)
   goto skip;

  if (vma->vm_start > start)
   start = vma->vm_start;
  vma_end = min(end, vma->vm_end);

  new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
  vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
         new_flags,
         (struct vm_userfaultfd_ctx){ctx},
         /* give_up_on_oom = */false);
  if (IS_ERR(vma))
   return PTR_ERR(vma);

  /*
* In the vma_merge() successful mprotect-like case 8:
* the next vma was merged into the current one and
* the current one has not been updated yet.
*/
  userfaultfd_set_ctx(vma, ctx, vm_flags);

  if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
   hugetlb_unshare_all_pmds(vma);

skip:
  prev = vma;
  start = vma->vm_end;
}

return 0;
}

void userfaultfd_release_new(struct userfaultfd_ctx *ctx)
{
struct mm_struct *mm = ctx->mm;
struct vm_area_struct *vma;
VMA_ITERATOR(vmi, mm, 0);

/* the various vma->vm_userfaultfd_ctx still points to it */
mmap_write_lock(mm);
for_each_vma(vmi, vma) {
  if (vma->vm_userfaultfd_ctx.ctx == ctx)
   userfaultfd_reset_ctx(vma);
}
mmap_write_unlock(mm);
}

void userfaultfd_release_all(struct mm_struct *mm,
        struct userfaultfd_ctx *ctx)
{
struct vm_area_struct *vma, *prev;
VMA_ITERATOR(vmi, mm, 0);

if (!mmget_not_zero(mm))
  return;

/*
* Flush page faults out of all CPUs. NOTE: all page faults
* must be retried without returning VM_FAULT_SIGBUS if
* userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
* changes while handle_userfault released the mmap_lock. So
* it's critical that released is set to true (above), before
* taking the mmap_lock for writing.
*/
mmap_write_lock(mm);
prev = NULL;
for_each_vma(vmi, vma) {
  cond_resched();
  VM_WARN_ON_ONCE(!!vma->vm_userfaultfd_ctx.ctx ^
    !!(vma->vm_flags & __VM_UFFD_FLAGS));
  if (vma->vm_userfaultfd_ctx.ctx != ctx) {
   prev = vma;
   continue;
  }

  vma = userfaultfd_clear_vma(&vmi, prev, vma,
         vma->vm_start, vma->vm_end);
  prev = vma;
}
mmap_write_unlock(mm);
mmput(mm);
}

quality79%

¤ Dauer der Verarbeitung: 0.64 Sekunden (vorverarbeitet) ¤

Normalansicht

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.