Messages in this thread |  | | Date | Tue, 23 Sep 2025 02:10:43 +0000 | | From | Wei Yang <> | | Subject | Re: [PATCH 1/1] mm/thp: fix MTE tag mismatch when replacing zero-filled subpages |
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On Mon, Sep 22, 2025 at 10:14:58AM +0800, 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>
Nice catch.
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
-- Wei Yang Help you, Help me
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