Messages in this thread |  | | Date | Mon, 22 Sep 2025 10:24:01 +0200 | | Subject | Re: [PATCH 1/1] mm/thp: fix MTE tag mismatch when replacing zero-filled subpages | | From | Usama Arif <> |
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On 22/09/2025 03:14, Lance Yang wrote: > From: Lance Yang <lance.yang@linux.dev> > > When both THP and MTE are enabled, splitting a THP and replacing its > zero-filled subpages with the shared zeropage can cause MTE tag mismatch > faults in userspace. > > Remapping zero-filled subpages to the shared zeropage is unsafe, as the > zeropage has a fixed tag of zero, which may not match the tag expected by > the userspace pointer. > > KSM already avoids this problem by using memcmp_pages(), which on arm64 > intentionally reports MTE-tagged pages as non-identical to prevent unsafe > merging. > > As suggested by David[1], this patch adopts the same pattern, replacing the > memchr_inv() byte-level check with a call to pages_identical(). This > leverages existing architecture-specific logic to determine if a page is > truly identical to the shared zeropage. > > Having both the THP shrinker and KSM rely on pages_identical() makes the > design more future-proof, IMO. Instead of handling quirks in generic code, > we just let the architecture decide what makes two pages identical. > > [1] https://lore.kernel.org/all/ca2106a3-4bb2-4457-81af-301fd99fbef4@redhat.com > > Cc: <stable@vger.kernel.org> > Reported-by: Qun-wei Lin <Qun-wei.Lin@mediatek.com> > Closes: https://lore.kernel.org/all/a7944523fcc3634607691c35311a5d59d1a3f8d4.camel@mediatek.com > Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") > Suggested-by: David Hildenbrand <david@redhat.com> > Signed-off-by: Lance Yang <lance.yang@linux.dev> > --- > Tested on x86_64 and on QEMU for arm64 (with and without MTE support), > and the fix works as expected. > > mm/huge_memory.c | 15 +++------------ > mm/migrate.c | 8 +------- > 2 files changed, 4 insertions(+), 19 deletions(-) >
Thanks for the fix!
Acked-by: Usama Arif <usamaarif642@gmail.com>
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