From: David Hildenbrand Date: Wed, 5 Apr 2023 16:02:36 +0000 (+0200) Subject: mm/userfaultfd: don't consider uffd-wp bit of writable migration entries X-Git-Tag: v6.6.7~2970^2~118 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=27da93d8e6d5633ac065c9316afc0f0240303c0a;p=platform%2Fkernel%2Flinux-starfive.git 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 Reviewed-by: Peter Xu Cc: Muhammad Usama Anjum Signed-off-by: Andrew Morton --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 03d7890..0dbce09 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; } diff --git a/mm/mprotect.c b/mm/mprotect.c index 20419415..92d3d3c 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -223,8 +223,6 @@ static long change_pte_range(struct mmu_gather *tlb, newpte = swp_entry_to_pte(entry); if (pte_swp_soft_dirty(oldpte)) newpte = pte_swp_mksoft_dirty(newpte); - if (pte_swp_uffd_wp(oldpte)) - newpte = pte_swp_mkuffd_wp(newpte); } else if (is_writable_device_private_entry(entry)) { /* * We do not preserve soft-dirtiness. See