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Rao" , Christian Borntraeger , Sven Schnelle , "David S. Miller" , Andreas Larsson , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20240501143310.1381675-1-ryan.roberts@arm.com> <3d88297b-ce6f-4b97-8a25-75f0987af6fd@redhat.com> <60739cf6-42ff-44c7-8e33-6c42eed71a66@arm.com> Content-Language: en-US From: Felix Kuehling Organization: AMD Inc. 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024-05-02 09:47, Ryan Roberts wrote: > On 02/05/2024 14:08, David Hildenbrand wrote: >> On 01.05.24 16:33, Ryan Roberts wrote: >>> __split_huge_pmd_locked() can be called for a present THP, devmap or >>> (non-present) migration entry. It calls pmdp_invalidate() >>> unconditionally on the pmdp and only determines if it is present or not >>> based on the returned old pmd. This is a problem for the migration entry >>> case because pmd_mkinvalid(), called by pmdp_invalidate() must only be >>> called for a present pmd. >>> >>> On arm64 at least, pmd_mkinvalid() will mark the pmd such that any >>> future call to pmd_present() will return true. And therefore any >>> lockless pgtable walker could see the migration entry pmd in this state >>> and start interpretting the fields as if it were present, leading to >>> BadThings (TM). GUP-fast appears to be one such lockless pgtable walker. >>> >>> x86 does not suffer the above problem, but instead pmd_mkinvalid() will >>> corrupt the offset field of the swap entry within the swap pte. See link >>> below for discussion of that problem. >> Could that explain: >> >> https://lore.kernel.org/all/YjoGbhreg8lGCGIJ@linutronix.de/ >> >> Where the PFN of a migration entry might have been corrupted? > Ahh interesting! Yes, it seems to fit... > >> Ccing Felix > Are you able to reliably reproduce the bug, Felix? If so, would you mind trying > with this patch to see if it goes away? Sorry, this question got lost and I found it while cleaning my inbox. The team that ran into this problems reported that it was a one-off failure. They didn't see this problem again. So I can't help with verifying the fix. Regards,   Felix > >> Patch itself looks good to me >> >> Acked-by: David Hildenbrand > Thanks! >