The patch titled
Subject: mm/userfaultfd: don't consider uffd-wp bit of writable migration entries
has been added to the -mm mm-unstable branch. Its filename is
mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/userfaultfd: don't consider uffd-wp bit of writable migration entries
Date: Wed, 5 Apr 2023 18:02:36 +0200
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@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 2 --
mm/mprotect.c | 2 --
2 files changed, 4 deletions(-)
--- a/mm/huge_memory.c~mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries
+++ a/mm/huge_memory.c
@@ -1845,8 +1845,6 @@ int change_huge_pmd(struct mmu_gather *t
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;
}
--- a/mm/mprotect.c~mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries
+++ a/mm/mprotect.c
@@ -223,8 +223,6 @@ static long change_pte_range(struct mmu_
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
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch
m68k-mm-use-correct-bit-number-in-_page_swp_exclusive-comment.patch
mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries.patch
