The patch titled
Subject: mm/hugetlb: make userfaultfd_huge_must_wait() safe to pmd unshare
has been added to the -mm mm-unstable branch. Its filename is
mm-hugetlb-make-userfaultfd_huge_must_wait-safe-to-pmd-unshare.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-make-userfaultfd_huge_must_wait-safe-to-pmd-unshare.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/hugetlb: make userfaultfd_huge_must_wait() safe to pmd unshare
Date: Fri, 16 Dec 2022 10:52:17 -0500
We can take the hugetlb walker lock, here taking vma lock directly.
Link: https://lkml.kernel.org/r/20221216155217.2043700-1-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
--- a/fs/userfaultfd.c~mm-hugetlb-make-userfaultfd_huge_must_wait-safe-to-pmd-unshare
+++ a/fs/userfaultfd.c
@@ -376,7 +376,8 @@ static inline unsigned int userfaultfd_g
*/
vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
{
- struct mm_struct *mm = vmf->vma->vm_mm;
+ struct vm_area_struct *vma = vmf->vma;
+ struct mm_struct *mm = vma->vm_mm;
struct userfaultfd_ctx *ctx;
struct userfaultfd_wait_queue uwq;
vm_fault_t ret = VM_FAULT_SIGBUS;
@@ -403,7 +404,7 @@ vm_fault_t handle_userfault(struct vm_fa
*/
mmap_assert_locked(mm);
- ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
+ ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx)
goto out;
@@ -493,6 +494,15 @@ vm_fault_t handle_userfault(struct vm_fa
blocking_state = userfaultfd_get_blocking_state(vmf->flags);
+ /*
+ * Take the vma lock now, in order to safely call
+ * userfaultfd_huge_must_wait() later. Since acquiring the
+ * (sleepable) vma lock can modify the current task state, that
+ * must be before explicitly calling set_current_state().
+ */
+ if (is_vm_hugetlb_page(vma))
+ hugetlb_vma_lock_read(vma);
+
spin_lock_irq(&ctx->fault_pending_wqh.lock);
/*
* After the __add_wait_queue the uwq is visible to userland
@@ -507,13 +517,15 @@ vm_fault_t handle_userfault(struct vm_fa
set_current_state(blocking_state);
spin_unlock_irq(&ctx->fault_pending_wqh.lock);
- if (!is_vm_hugetlb_page(vmf->vma))
+ if (!is_vm_hugetlb_page(vma))
must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
reason);
else
- must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
+ must_wait = userfaultfd_huge_must_wait(ctx, vma,
vmf->address,
vmf->flags, reason);
+ if (is_vm_hugetlb_page(vma))
+ hugetlb_vma_unlock_read(vma);
mmap_read_unlock(mm);
if (likely(must_wait && !READ_ONCE(ctx->released))) {
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-uffd-fix-pte-marker-when-fork-without-fork-event.patch
mm-fix-a-few-rare-cases-of-using-swapin-error-pte-marker.patch
mm-uffd-always-wr-protect-pte-in-ptepmd_mkuffd_wp.patch
mm-hugetlb-let-vma_offset_start-to-return-start.patch
mm-hugetlb-dont-wait-for-migration-entry-during-follow-page.patch
mm-hugetlb-document-huge_pte_offset-usage.patch
mm-hugetlb-move-swap-entry-handling-into-vma-lock-when-faulted.patch
mm-hugetlb-make-userfaultfd_huge_must_wait-safe-to-pmd-unshare.patch
mm-hugetlb-make-hugetlb_follow_page_mask-safe-to-pmd-unshare.patch
mm-hugetlb-make-follow_hugetlb_page-safe-to-pmd-unshare.patch
mm-hugetlb-make-walk_hugetlb_range-safe-to-pmd-unshare.patch
mm-hugetlb-introduce-hugetlb_walk.patch
