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authorDavid Hildenbrand <david@redhat.com>2023-04-05 18:02:36 +0200
committerAndrew Morton <akpm@linux-foundation.org>2023-04-18 16:29:53 -0700
commit27da93d8e6d5633ac065c9316afc0f0240303c0a (patch)
tree76459528309a99501acba14b0f29a1efce47e14f /mm/huge_memory.c
parent2bd7f621130b47cab8bed82234cac1f9f105efb7 (diff)
mm/userfaultfd: don't consider uffd-wp bit of writable migration entries
If we end up with a writable migration entry that has the uffd-wp bit set, we already messed up: the source PTE/PMD was writable, which means we could have modified the page without notifying uffd first. Setting the uffd-wp bit always implies converting migration entries to !writable migration entries. Commit 8f34f1eac382 ("mm/userfaultfd: fix uffd-wp special cases for fork()") documents that "3. Forget to carry over uffd-wp bit for a write migration huge pmd entry", but it doesn't really say why that should be relevant. So let's remove that code to avoid hiding an eventual underlying issue (in the future, we might want to warn when creating writable migration entries that have the uffd-wp bit set -- or even better when turning a PTE writable that still has the uffd-wp bit set). This now matches the handling for hugetlb migration entries in hugetlb_change_protection(). In copy_huge_pmd()/copy_nonpresent_pte()/copy_hugetlb_page_range(), we still transfer the uffd-bit also for writable migration entries, but simply because we have unified handling for "writable" and "readable-exclusive" migration entries, and we care about transferring the uffd-wp bit for the latter. Link: https://lkml.kernel.org/r/20230405160236.587705-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Peter Xu <peterx@redhat.com> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c2
1 files changed, 0 insertions, 2 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 03d78901a7a7..0dbce09916c4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1845,8 +1845,6 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
newpmd = swp_entry_to_pmd(entry);
if (pmd_swp_soft_dirty(*pmd))
newpmd = pmd_swp_mksoft_dirty(newpmd);
- if (pmd_swp_uffd_wp(*pmd))
- newpmd = pmd_swp_mkuffd_wp(newpmd);
} else {
newpmd = *pmd;
}