The patch titled
Subject: mm: check against orig_pte for finish_fault()
has been added to the -mm tree. Its filename is
mm-check-against-orig_pte-for-finish_fault.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-check-against-orig_pte-for-finish_fault.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-check-against-orig_pte-for-finish_fault.patch
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------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm: check against orig_pte for finish_fault()
We used to check against none pte in finish_fault(), with the assumption
that the orig_pte is always none pte.
This change prepares us to be able to call do_fault() on !none ptes. For
example, we should allow that to happen for pte marker so that we can
restore information out of the pte markers.
Let's change the "pte_none" check into detecting changes since we fetched
orig_pte. One trivial thing to take care of here is, when pmd==NULL for
the pgtable we may not initialize orig_pte at all in handle_pte_fault().
By default orig_pte will be all zeros however the problem is not all
architectures are using all-zeros for a none pte. pte_clear() will be the
right thing to use here so that we'll always have a valid orig_pte value
for the whole handle_pte_fault() call.
Link: https://lkml.kernel.org/r/20220405014836.14077-1-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/memory.c~mm-check-against-orig_pte-for-finish_fault
+++ a/mm/memory.c
@@ -4237,7 +4237,7 @@ vm_fault_t finish_fault(struct vm_fault
vmf->address, &vmf->ptl);
ret = 0;
/* Re-check under ptl */
- if (likely(pte_none(*vmf->pte)))
+ if (likely(pte_same(*vmf->pte, vmf->orig_pte)))
do_set_pte(vmf, page, vmf->address);
else
ret = VM_FAULT_NOPAGE;
@@ -4705,6 +4705,13 @@ static vm_fault_t handle_pte_fault(struc
* concurrent faults and from rmap lookups.
*/
vmf->pte = NULL;
+ /*
+ * Always initialize orig_pte. This matches with below
+ * code to have orig_pte to be the none pte if pte==NULL.
+ * This makes the rest code to be always safe to reference
+ * it, e.g. in finish_fault() we'll detect pte changes.
+ */
+ pte_clear(vmf->vma->vm_mm, vmf->address, &vmf->orig_pte);
} else {
/*
* If a huge pmd materialized under us just retry later. Use
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-introduce-pte_marker-swap-entry.patch
mm-teach-core-mm-about-pte-markers.patch
mm-check-against-orig_pte-for-finish_fault.patch
mm-uffd-pte_marker_uffd_wp.patch
mm-shmem-take-care-of-uffdio_copy_mode_wp.patch
mm-shmem-handle-uffd-wp-special-pte-in-page-fault-handler.patch
mm-shmem-persist-uffd-wp-bit-across-zapping-for-file-backed.patch
mm-shmem-allow-uffd-wr-protect-none-pte-for-file-backed-mem.patch
mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps.patch
mm-shmem-handle-uffd-wp-during-fork.patch
mm-hugetlb-introduce-huge-pte-version-of-uffd-wp-helpers.patch
mm-hugetlb-hook-page-faults-for-uffd-write-protection.patch
mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch
mm-hugetlb-handle-uffdio_writeprotect.patch
mm-hugetlb-handle-pte-markers-in-page-faults.patch
mm-hugetlb-allow-uffd-wr-protect-none-ptes.patch
mm-hugetlb-only-drop-uffd-wp-special-pte-if-required.patch
mm-hugetlb-handle-uffd-wp-during-fork.patch
mm-khugepaged-dont-recycle-vma-pgtable-if-uffd-wp-registered.patch
mm-pagemap-recognize-uffd-wp-bit-for-shmem-hugetlbfs.patch
mm-uffd-enable-write-protection-for-shmem-hugetlbfs.patch
mm-enable-pte-markers-by-default.patch
selftests-uffd-enable-uffd-wp-for-shmem-hugetlbfs.patch
