linux-IllusionX/mm/userfaultfd.c
Jann Horn 4828d207dc userfaultfd: don't BUG_ON() if khugepaged yanks our page table
Since khugepaged was changed to allow retracting page tables in file
mappings without holding the mmap lock, these BUG_ON()s are wrong - get
rid of them.

We could also remove the preceding "if (unlikely(...))" block, but then we
could reach pte_offset_map_lock() with transhuge pages not just for file
mappings but also for anonymous mappings - which would probably be fine
but I think is not necessarily expected.

Link: https://lkml.kernel.org/r/20240813-uffd-thp-flip-fix-v2-2-5efa61078a41@google.com
Fixes: 1d65b771bc ("mm/khugepaged: retract_page_tables() without mmap or vma lock")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-09-01 17:59:00 -07:00

1765 lines
46 KiB
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"
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)) {
/*
* We cannot use vma_start_read() as it may fail due to
* false locked (see comment in vma_start_read()). We
* can avoid that by directly locking vm_lock under
* mmap_lock, which guarantees that nobody can lock the
* vma for write (vma_start_write()) under us.
*/
down_read(&vma->vm_lock->lock);
}
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, false);
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, &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) {
BUG_ON(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);
BUG_ON(!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
BUG_ON(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);
BUG_ON(copied < 0);
BUG_ON(err > 0);
BUG_ON(!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:
*/
BUG_ON(dst_start & ~PAGE_MASK);
BUG_ON(len & ~PAGE_MASK);
/* Does the address range wrap, or is the span zero-sized? */
BUG_ON(src_start + len <= src_start);
BUG_ON(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;
BUG_ON(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) ||
pmd_devmap(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);
BUG_ON(!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
BUG_ON(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);
BUG_ON(copied < 0);
BUG_ON(err > 0);
BUG_ON(!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:
*/
BUG_ON(start & ~PAGE_MASK);
BUG_ON(len & ~PAGE_MASK);
/* Does the address range wrap, or is the span zero-sized? */
BUG_ON(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 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,
spinlock_t *dst_ptl, spinlock_t *src_ptl,
struct folio *src_folio)
{
int err = 0;
double_pt_lock(dst_ptl, src_ptl);
if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
!pte_same(ptep_get(dst_pte), orig_dst_pte)) {
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 = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
/* Follow mremap() behavior and treat the entry dirty after the move */
orig_dst_pte = pte_mkwrite(pte_mkdirty(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,
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,
spinlock_t *dst_ptl, spinlock_t *src_ptl)
{
if (!pte_swp_exclusive(orig_src_pte))
return -EBUSY;
double_pt_lock(dst_ptl, src_ptl);
if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
!pte_same(ptep_get(dst_pte), orig_dst_pte)) {
double_pt_unlock(dst_ptl, src_ptl);
return -EAGAIN;
}
orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
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,
spinlock_t *dst_ptl, spinlock_t *src_ptl)
{
pte_t zero_pte;
double_pt_lock(dst_ptl, src_ptl);
if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
!pte_same(ptep_get(dst_pte), orig_dst_pte)) {
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;
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;
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:
dst_pte = pte_offset_map_nolock(mm, dst_pmd, dst_addr, &dst_ptl);
/* Retry if a huge pmd materialized from under us */
if (unlikely(!dst_pte)) {
err = -EAGAIN;
goto out;
}
src_pte = pte_offset_map_nolock(mm, src_pmd, src_addr, &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 (WARN_ON_ONCE(pmd_none(*dst_pmd)) || WARN_ON_ONCE(pmd_none(*src_pmd)) ||
WARN_ON_ONCE(pmd_trans_huge(*dst_pmd)) || WARN_ON_ONCE(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_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;
/*
* 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;
}
folio_get(folio);
src_folio = folio;
src_folio_pte = orig_src_pte;
spin_unlock(src_ptl);
if (!folio_trylock(src_folio)) {
pte_unmap(&orig_src_pte);
pte_unmap(&orig_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(&orig_src_pte);
pte_unmap(&orig_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(&orig_src_pte);
pte_unmap(&orig_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_ptl, src_ptl, src_folio);
} else {
entry = pte_to_swp_entry(orig_src_pte);
if (non_swap_entry(entry)) {
if (is_migration_entry(entry)) {
pte_unmap(&orig_src_pte);
pte_unmap(&orig_dst_pte);
src_pte = dst_pte = NULL;
migration_entry_wait(mm, src_pmd, src_addr);
err = -EAGAIN;
} else
err = -EFAULT;
goto out;
}
err = move_swap_pte(mm, dst_addr, src_addr,
dst_pte, src_pte,
orig_dst_pte, orig_src_pte,
dst_ptl, src_ptl);
}
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);
}
if (dst_pte)
pte_unmap(dst_pte);
if (src_pte)
pte_unmap(src_pte);
mmu_notifier_invalidate_range_end(&range);
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) {
/*
* See comment in uffd_lock_vma() as to why not using
* vma_start_read() here.
*/
down_read(&(*dst_vmap)->vm_lock->lock);
if (*dst_vmap != *src_vmap)
down_read_nested(&(*src_vmap)->vm_lock->lock,
SINGLE_DEPTH_NESTING);
}
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. */
if (WARN_ON_ONCE(src_start & ~PAGE_MASK) ||
WARN_ON_ONCE(dst_start & ~PAGE_MASK) ||
WARN_ON_ONCE(len & ~PAGE_MASK))
goto out;
/* Does the address range wrap, or is the span zero-sized? */
if (WARN_ON_ONCE(src_start + len <= src_start) ||
WARN_ON_ONCE(dst_start + len <= dst_start))
goto out;
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) {
if (pmd_devmap(*src_pmd)) {
spin_unlock(ptl);
err = -ENOENT;
break;
}
/* 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)) {
struct folio *folio = pmd_folio(*src_pmd);
if (!folio || (!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(moved < 0);
VM_WARN_ON(err > 0);
VM_WARN_ON(!moved && !err);
return moved ? moved : err;
}