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Subject[PATCH 19/21] userfaultfd: remap_pages: UFFDIO_REMAP preparation
Date
remap_pages is the lowlevel mm helper needed to implement
UFFDIO_REMAP.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
include/linux/userfaultfd_k.h | 17 ++
mm/huge_memory.c | 120 ++++++++++
mm/userfaultfd.c | 526 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 663 insertions(+)

diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 587480a..3c39a4f 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -36,6 +36,23 @@ extern ssize_t mfill_zeropage(struct mm_struct *dst_mm,
unsigned long dst_start,
unsigned long len);

+/* remap_pages */
+extern void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2);
+extern void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2);
+extern ssize_t remap_pages(struct mm_struct *dst_mm,
+ struct mm_struct *src_mm,
+ unsigned long dst_start,
+ unsigned long src_start,
+ unsigned long len, __u64 flags);
+extern int remap_pages_huge_pmd(struct mm_struct *dst_mm,
+ struct mm_struct *src_mm,
+ pmd_t *dst_pmd, pmd_t *src_pmd,
+ pmd_t dst_pmdval,
+ struct vm_area_struct *dst_vma,
+ struct vm_area_struct *src_vma,
+ unsigned long dst_addr,
+ unsigned long src_addr);
+
/* mm helpers */
static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
struct vm_userfaultfd_ctx vm_ctx)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1e25cb3..08c8afc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1531,6 +1531,124 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
return ret;
}

+#ifdef CONFIG_USERFAULTFD
+/*
+ * The PT lock for src_pmd and the mmap_sem for reading are held by
+ * the caller, but it must return after releasing the
+ * page_table_lock. We're guaranteed the src_pmd is a pmd_trans_huge
+ * until the PT lock of the src_pmd is released. Just move the page
+ * from src_pmd to dst_pmd if possible. Return zero if succeeded in
+ * moving the page, -EAGAIN if it needs to be repeated by the caller,
+ * or other errors in case of failure.
+ */
+int remap_pages_huge_pmd(struct mm_struct *dst_mm,
+ struct mm_struct *src_mm,
+ pmd_t *dst_pmd, pmd_t *src_pmd,
+ pmd_t dst_pmdval,
+ struct vm_area_struct *dst_vma,
+ struct vm_area_struct *src_vma,
+ unsigned long dst_addr,
+ unsigned long src_addr)
+{
+ pmd_t _dst_pmd, src_pmdval;
+ struct page *src_page;
+ struct anon_vma *src_anon_vma, *dst_anon_vma;
+ spinlock_t *src_ptl, *dst_ptl;
+ pgtable_t pgtable;
+
+ src_pmdval = *src_pmd;
+ src_ptl = pmd_lockptr(src_mm, src_pmd);
+
+ BUG_ON(!pmd_trans_huge(src_pmdval));
+ BUG_ON(pmd_trans_splitting(src_pmdval));
+ BUG_ON(!pmd_none(dst_pmdval));
+ BUG_ON(!spin_is_locked(src_ptl));
+ BUG_ON(!rwsem_is_locked(&src_mm->mmap_sem));
+ BUG_ON(!rwsem_is_locked(&dst_mm->mmap_sem));
+
+ src_page = pmd_page(src_pmdval);
+ BUG_ON(!PageHead(src_page));
+ BUG_ON(!PageAnon(src_page));
+ if (unlikely(page_mapcount(src_page) != 1)) {
+ spin_unlock(src_ptl);
+ return -EBUSY;
+ }
+
+ get_page(src_page);
+ spin_unlock(src_ptl);
+
+ mmu_notifier_invalidate_range_start(src_mm, src_addr,
+ src_addr + HPAGE_PMD_SIZE);
+
+ /* block all concurrent rmap walks */
+ lock_page(src_page);
+
+ /*
+ * split_huge_page walks the anon_vma chain without the page
+ * lock. Serialize against it with the anon_vma lock, the page
+ * lock is not enough.
+ */
+ src_anon_vma = page_get_anon_vma(src_page);
+ if (!src_anon_vma) {
+ unlock_page(src_page);
+ put_page(src_page);
+ mmu_notifier_invalidate_range_end(src_mm, src_addr,
+ src_addr + HPAGE_PMD_SIZE);
+ return -EAGAIN;
+ }
+ anon_vma_lock_write(src_anon_vma);
+
+ dst_ptl = pmd_lockptr(dst_mm, dst_pmd);
+ double_pt_lock(src_ptl, dst_ptl);
+ if (unlikely(!pmd_same(*src_pmd, src_pmdval) ||
+ !pmd_same(*dst_pmd, dst_pmdval) ||
+ page_mapcount(src_page) != 1)) {
+ double_pt_unlock(src_ptl, dst_ptl);
+ anon_vma_unlock_write(src_anon_vma);
+ put_anon_vma(src_anon_vma);
+ unlock_page(src_page);
+ put_page(src_page);
+ mmu_notifier_invalidate_range_end(src_mm, src_addr,
+ src_addr + HPAGE_PMD_SIZE);
+ return -EAGAIN;
+ }
+
+ BUG_ON(!PageHead(src_page));
+ BUG_ON(!PageAnon(src_page));
+ /* the PT lock is enough to keep the page pinned now */
+ put_page(src_page);
+
+ dst_anon_vma = (void *) dst_vma->anon_vma + PAGE_MAPPING_ANON;
+ ACCESS_ONCE(src_page->mapping) = (struct address_space *) dst_anon_vma;
+ ACCESS_ONCE(src_page->index) = linear_page_index(dst_vma, dst_addr);
+
+ if (!pmd_same(pmdp_clear_flush(src_vma, src_addr, src_pmd),
+ src_pmdval))
+ BUG();
+ _dst_pmd = mk_huge_pmd(src_page, dst_vma->vm_page_prot);
+ _dst_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma);
+ set_pmd_at(dst_mm, dst_addr, dst_pmd, _dst_pmd);
+
+ pgtable = pgtable_trans_huge_withdraw(src_mm, src_pmd);
+ pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
+ if (dst_mm != src_mm) {
+ add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+ add_mm_counter(src_mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+ }
+ double_pt_unlock(src_ptl, dst_ptl);
+
+ anon_vma_unlock_write(src_anon_vma);
+ put_anon_vma(src_anon_vma);
+
+ /* unblock rmap walks */
+ unlock_page(src_page);
+
+ mmu_notifier_invalidate_range_end(src_mm, src_addr,
+ src_addr + HPAGE_PMD_SIZE);
+ return 0;
+}
+#endif /* CONFIG_USERFAULTFD */
+
/*
* Returns 1 if a given pmd maps a stable (not under splitting) thp.
* Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
@@ -2484,6 +2602,8 @@ static void collapse_huge_page(struct mm_struct *mm,
* Prevent all access to pagetables with the exception of
* gup_fast later hanlded by the ptep_clear_flush and the VM
* handled by the anon_vma lock + PG_lock.
+ *
+ * remap_pages is prevented to race as well thanks to the mmap_sem.
*/
down_write(&mm->mmap_sem);
if (unlikely(khugepaged_test_exit(mm)))
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 3f4c0ef..49521af 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -265,3 +265,529 @@ ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
{
return __mcopy_atomic(dst_mm, start, 0, len, true);
}
+
+void double_pt_lock(spinlock_t *ptl1,
+ spinlock_t *ptl2)
+ __acquires(ptl1)
+ __acquires(ptl2)
+{
+ spinlock_t *ptl_tmp;
+
+ if (ptl1 > ptl2) {
+ /* exchange ptl1 and ptl2 */
+ ptl_tmp = ptl1;
+ ptl1 = ptl2;
+ ptl2 = ptl_tmp;
+ }
+ /* 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);
+}
+
+/*
+ * The mmap_sem 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 remap_pages_pte(struct mm_struct *dst_mm,
+ struct mm_struct *src_mm,
+ pte_t *dst_pte, pte_t *src_pte, pmd_t *src_pmd,
+ struct vm_area_struct *dst_vma,
+ struct vm_area_struct *src_vma,
+ unsigned long dst_addr,
+ unsigned long src_addr,
+ spinlock_t *dst_ptl,
+ spinlock_t *src_ptl,
+ __u64 mode)
+{
+ struct page *src_page;
+ swp_entry_t entry;
+ pte_t orig_src_pte, orig_dst_pte;
+ struct anon_vma *src_anon_vma, *dst_anon_vma;
+
+ spin_lock(dst_ptl);
+ orig_dst_pte = *dst_pte;
+ spin_unlock(dst_ptl);
+ if (!pte_none(orig_dst_pte))
+ return -EEXIST;
+
+ spin_lock(src_ptl);
+ orig_src_pte = *src_pte;
+ spin_unlock(src_ptl);
+ if (pte_none(orig_src_pte)) {
+ if (!(mode & UFFDIO_REMAP_MODE_ALLOW_SRC_HOLES))
+ return -ENOENT;
+ else
+ /* nothing to do to remap an hole */
+ return 0;
+ }
+
+ if (pte_present(orig_src_pte)) {
+ /*
+ * 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, *src_pte)) {
+ spin_unlock(src_ptl);
+ return -EAGAIN;
+ }
+ src_page = vm_normal_page(src_vma, src_addr, orig_src_pte);
+ if (!src_page || !PageAnon(src_page) ||
+ page_mapcount(src_page) != 1) {
+ spin_unlock(src_ptl);
+ return -EBUSY;
+ }
+
+ get_page(src_page);
+ spin_unlock(src_ptl);
+
+ /* block all concurrent rmap walks */
+ lock_page(src_page);
+
+ /*
+ * page_referenced_anon walks the anon_vma chain
+ * without the page lock. Serialize against it with
+ * the anon_vma lock, the page lock is not enough.
+ */
+ src_anon_vma = page_get_anon_vma(src_page);
+ if (!src_anon_vma) {
+ /* page was unmapped from under us */
+ unlock_page(src_page);
+ put_page(src_page);
+ return -EAGAIN;
+ }
+ anon_vma_lock_write(src_anon_vma);
+
+ double_pt_lock(dst_ptl, src_ptl);
+
+ if (!pte_same(*src_pte, orig_src_pte) ||
+ !pte_same(*dst_pte, orig_dst_pte) ||
+ page_mapcount(src_page) != 1) {
+ double_pt_unlock(dst_ptl, src_ptl);
+ anon_vma_unlock_write(src_anon_vma);
+ put_anon_vma(src_anon_vma);
+ unlock_page(src_page);
+ put_page(src_page);
+ return -EAGAIN;
+ }
+
+ BUG_ON(!PageAnon(src_page));
+ /* the PT lock is enough to keep the page pinned now */
+ put_page(src_page);
+
+ dst_anon_vma = (void *) dst_vma->anon_vma + PAGE_MAPPING_ANON;
+ ACCESS_ONCE(src_page->mapping) = ((struct address_space *)
+ dst_anon_vma);
+ ACCESS_ONCE(src_page->index) = linear_page_index(dst_vma,
+ dst_addr);
+
+ if (!pte_same(ptep_clear_flush(src_vma, src_addr, src_pte),
+ orig_src_pte))
+ BUG();
+
+ orig_dst_pte = mk_pte(src_page, dst_vma->vm_page_prot);
+ orig_dst_pte = maybe_mkwrite(pte_mkdirty(orig_dst_pte),
+ dst_vma);
+
+ set_pte_at(dst_mm, dst_addr, dst_pte, orig_dst_pte);
+
+ if (dst_mm != src_mm) {
+ inc_mm_counter(dst_mm, MM_ANONPAGES);
+ dec_mm_counter(src_mm, MM_ANONPAGES);
+ }
+
+ double_pt_unlock(dst_ptl, src_ptl);
+
+ anon_vma_unlock_write(src_anon_vma);
+ put_anon_vma(src_anon_vma);
+
+ /* unblock rmap walks */
+ unlock_page(src_page);
+
+ mmu_notifier_invalidate_page(src_mm, src_addr);
+ } else {
+ entry = pte_to_swp_entry(orig_src_pte);
+ if (non_swap_entry(entry)) {
+ if (is_migration_entry(entry)) {
+ migration_entry_wait(src_mm, src_pmd,
+ src_addr);
+ return -EAGAIN;
+ }
+ return -EFAULT;
+ }
+
+ if (swp_entry_swapcount(entry) != 1)
+ return -EBUSY;
+
+ double_pt_lock(dst_ptl, src_ptl);
+
+ if (!pte_same(*src_pte, orig_src_pte) ||
+ !pte_same(*dst_pte, orig_dst_pte) ||
+ swp_entry_swapcount(entry) != 1) {
+ double_pt_unlock(dst_ptl, src_ptl);
+ return -EAGAIN;
+ }
+
+ if (pte_val(ptep_get_and_clear(src_mm, src_addr, src_pte)) !=
+ pte_val(orig_src_pte))
+ BUG();
+ set_pte_at(dst_mm, dst_addr, dst_pte, orig_src_pte);
+
+ if (dst_mm != src_mm) {
+ inc_mm_counter(dst_mm, MM_ANONPAGES);
+ dec_mm_counter(src_mm, MM_ANONPAGES);
+ }
+
+ double_pt_unlock(dst_ptl, src_ptl);
+ }
+
+ return 0;
+}
+
+/**
+ * remap_pages - remap arbitrary anonymous pages of an existing vma
+ * @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
+ *
+ * remap_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 is the ideal mechanism to handle userspace page faults. Normally
+ * the destination vma will have VM_USERFAULT set with
+ * madvise(MADV_USERFAULT) while the source vma will have VM_DONTCOPY
+ * set with madvise(MADV_DONTFORK).
+ *
+ * The thread receiving the page during the userland page fault
+ * (MADV_USERFAULT) 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 remap_pages() to fail with -EBUSY if the
+ * process forks before remap_pages() is called), then it will call
+ * remap_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,
+ * remap_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 remap_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 succesful. 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 remap_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_REMAP_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 page lock (for example split_huge_page and
+ * page_referenced_anon), they will have to verify if the
+ * page->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
+ * remap_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 remap_pages(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+ unsigned long dst_start, unsigned long src_start,
+ unsigned long len, __u64 mode)
+{
+ struct vm_area_struct *src_vma, *dst_vma;
+ long err = -EINVAL;
+ pmd_t *src_pmd, *dst_pmd;
+ pte_t *src_pte, *dst_pte;
+ spinlock_t *dst_ptl, *src_ptl;
+ unsigned long src_addr, dst_addr;
+ int thp_aligned = -1;
+ ssize_t moved = 0;
+
+ /*
+ * Sanitize the command parameters:
+ */
+ BUG_ON(src_start & ~PAGE_MASK);
+ 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);
+
+ /*
+ * Because these are read sempahores there's no risk of lock
+ * inversion.
+ */
+ down_read(&dst_mm->mmap_sem);
+ if (dst_mm != src_mm)
+ down_read(&src_mm->mmap_sem);
+
+ /*
+ * Make sure the vma is not shared, that the src and dst remap
+ * ranges are both valid and fully within a single existing
+ * vma.
+ */
+ src_vma = find_vma(src_mm, src_start);
+ if (!src_vma || (src_vma->vm_flags & VM_SHARED))
+ goto out;
+ if (src_start < src_vma->vm_start ||
+ src_start + len > src_vma->vm_end)
+ goto out;
+
+ dst_vma = find_vma(dst_mm, dst_start);
+ if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
+ goto out;
+ if (dst_start < dst_vma->vm_start ||
+ dst_start + len > dst_vma->vm_end)
+ goto out;
+
+ if (pgprot_val(src_vma->vm_page_prot) !=
+ pgprot_val(dst_vma->vm_page_prot))
+ goto out;
+
+ /* only allow remapping if both are mlocked or both aren't */
+ if ((src_vma->vm_flags & VM_LOCKED) ^ (dst_vma->vm_flags & VM_LOCKED))
+ goto out;
+
+ /*
+ * Be strict and only allow remap_pages if either the src or
+ * dst range is registered in the userfaultfd to prevent
+ * userland errors going unnoticed. As far as the VM
+ * consistency is concerned, it would be perfectly safe to
+ * remove this check, but there's no useful usage for
+ * remap_pages ouside of userfaultfd registered ranges. This
+ * is after all why it is an ioctl belonging to the
+ * userfaultfd and not a syscall.
+ *
+ * Allow both vmas to be registered in the userfaultfd, just
+ * in case somebody finds a way to make such a case useful.
+ * Normally only one of the two vmas would be registered in
+ * the userfaultfd.
+ */
+ if (!dst_vma->vm_userfaultfd_ctx.ctx &&
+ !src_vma->vm_userfaultfd_ctx.ctx)
+ goto out;
+
+ /*
+ * FIXME: only allow remapping across anonymous vmas,
+ * tmpfs should be added.
+ */
+ if (src_vma->vm_ops || dst_vma->vm_ops)
+ goto out;
+
+ /*
+ * Ensure the dst_vma has a anon_vma or this page
+ * would get a NULL anon_vma when moved in the
+ * dst_vma.
+ */
+ err = -ENOMEM;
+ if (unlikely(anon_vma_prepare(dst_vma)))
+ goto out;
+
+ for (src_addr = src_start, dst_addr = dst_start;
+ src_addr < src_start + len; ) {
+ spinlock_t *ptl;
+ pmd_t dst_pmdval;
+ BUG_ON(dst_addr >= dst_start + len);
+ src_pmd = mm_find_pmd(src_mm, src_addr);
+ if (unlikely(!src_pmd)) {
+ if (!(mode & UFFDIO_REMAP_MODE_ALLOW_SRC_HOLES)) {
+ err = -ENOENT;
+ break;
+ } else {
+ src_pmd = mm_alloc_pmd(src_mm, src_addr);
+ if (unlikely(!src_pmd)) {
+ err = -ENOMEM;
+ break;
+ }
+ }
+ }
+ dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
+ if (unlikely(!dst_pmd)) {
+ err = -ENOMEM;
+ break;
+ }
+
+ dst_pmdval = pmd_read_atomic(dst_pmd);
+ /*
+ * If the dst_pmd is mapped as THP don't
+ * override it and just be strict.
+ */
+ if (unlikely(pmd_trans_huge(dst_pmdval))) {
+ err = -EEXIST;
+ break;
+ }
+ if (pmd_trans_huge_lock(src_pmd, src_vma, &ptl) == 1) {
+ /*
+ * Check if we can move the pmd without
+ * splitting it. First check the address
+ * alignment to be the same in src/dst. These
+ * checks don't actually need the PT lock but
+ * it's good to do it here to optimize this
+ * block away at build time if
+ * CONFIG_TRANSPARENT_HUGEPAGE is not set.
+ */
+ if (thp_aligned == -1)
+ thp_aligned = ((src_addr & ~HPAGE_PMD_MASK) ==
+ (dst_addr & ~HPAGE_PMD_MASK));
+ if (!thp_aligned || (src_addr & ~HPAGE_PMD_MASK) ||
+ !pmd_none(dst_pmdval) ||
+ src_start + len - src_addr < HPAGE_PMD_SIZE) {
+ spin_unlock(ptl);
+ /* Fall through */
+ split_huge_page_pmd(src_vma, src_addr,
+ src_pmd);
+ } else {
+ BUG_ON(dst_addr & ~HPAGE_PMD_MASK);
+ err = remap_pages_huge_pmd(dst_mm,
+ src_mm,
+ dst_pmd,
+ src_pmd,
+ dst_pmdval,
+ dst_vma,
+ src_vma,
+ dst_addr,
+ src_addr);
+ cond_resched();
+
+ if (!err) {
+ dst_addr += HPAGE_PMD_SIZE;
+ src_addr += HPAGE_PMD_SIZE;
+ moved += HPAGE_PMD_SIZE;
+ }
+
+ if ((!err || err == -EAGAIN) &&
+ fatal_signal_pending(current))
+ err = -EINTR;
+
+ if (err && err != -EAGAIN)
+ break;
+
+ continue;
+ }
+ }
+
+ if (pmd_none(*src_pmd)) {
+ if (!(mode & UFFDIO_REMAP_MODE_ALLOW_SRC_HOLES)) {
+ err = -ENOENT;
+ break;
+ } else {
+ if (unlikely(__pte_alloc(src_mm, src_vma,
+ src_pmd, src_addr))) {
+ err = -ENOMEM;
+ break;
+ }
+ }
+ }
+
+ /*
+ * We held the mmap_sem 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(pmd_trans_unstable(src_pmd))) {
+ err = -EFAULT;
+ break;
+ }
+
+ if (unlikely(pmd_none(dst_pmdval)) &&
+ unlikely(__pte_alloc(dst_mm, dst_vma, dst_pmd,
+ dst_addr))) {
+ err = -ENOMEM;
+ break;
+ }
+ /* If an huge pmd materialized from under us fail */
+ if (unlikely(pmd_trans_huge(*dst_pmd))) {
+ err = -EFAULT;
+ break;
+ }
+
+ BUG_ON(pmd_none(*dst_pmd));
+ BUG_ON(pmd_none(*src_pmd));
+ BUG_ON(pmd_trans_huge(*dst_pmd));
+ BUG_ON(pmd_trans_huge(*src_pmd));
+
+ dst_pte = pte_offset_map(dst_pmd, dst_addr);
+ src_pte = pte_offset_map(src_pmd, src_addr);
+ dst_ptl = pte_lockptr(dst_mm, dst_pmd);
+ src_ptl = pte_lockptr(src_mm, src_pmd);
+
+ err = remap_pages_pte(dst_mm, src_mm,
+ dst_pte, src_pte, src_pmd,
+ dst_vma, src_vma,
+ dst_addr, src_addr,
+ dst_ptl, src_ptl, mode);
+
+ pte_unmap(dst_pte);
+ pte_unmap(src_pte);
+ cond_resched();
+
+ if (!err) {
+ dst_addr += PAGE_SIZE;
+ src_addr += PAGE_SIZE;
+ moved += PAGE_SIZE;
+ }
+
+ if ((!err || err == -EAGAIN) &&
+ fatal_signal_pending(current))
+ err = -EINTR;
+
+ if (err && err != -EAGAIN)
+ break;
+ }
+
+out:
+ up_read(&dst_mm->mmap_sem);
+ if (dst_mm != src_mm)
+ up_read(&src_mm->mmap_sem);
+ BUG_ON(moved < 0);
+ BUG_ON(err > 0);
+ BUG_ON(!moved && !err);
+ return moved ? moved : err;
+}

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