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Wed, 04 Mar 2026 20:31:57 -0800 (PST) MIME-Version: 1.0 References: <20260303063751.2531716-1-pjaroszynski@nvidia.com> In-Reply-To: From: James Houghton Date: Wed, 4 Mar 2026 20:31:20 -0800 X-Gm-Features: AaiRm53dJeRWd8Nji1GYa5e5Z900_RBsGxiHxN9h3vB4MZepaklzjxRsMiu3r_c Message-ID: Subject: Re: [PATCH] arm64: contpte: fix set_access_flags() no-op check for SMMU/ATS faults To: Piotr Jaroszynski Cc: Ryan Roberts , Will Deacon , Catalin Marinas , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, Alistair Popple , Jason Gunthorpe , John Hubbard , Zi Yan , Breno Leitao , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: 6t87sngzwtyq39ma8bj1319h7rttqr1r X-Rspamd-Queue-Id: BAE6840006 X-Rspamd-Server: rspam03 X-HE-Tag: 1772685119-703878 X-HE-Meta: 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 vahfVmLo PfEjz014s+frK34EpWFKEO7YEI9VzEReQ6Gvb3TUBKsgrr6miS3+8ylabVLL1dgm2k6yFLM+WH/2e0d2v9En6A4Vf+vB7MZxt5TJ7kbMFhfeurEWwtWMRlalMiHxHv290Sl+5diQGvcOAIXNkfjzZxNosFLiZBmAlFUIqEKIU7MWFJkI+0V5PRUsrkRc+H6S3NydWV6L9MZ1dwKtQkh7Vr9pFt/e5rhSuNGO9d5cJLdWiDm0ib9jMruSMx4wVnH8HD1S/yHVtbSiGbQLxIIRUdI/BzEvb33jxZ1suQXJau8LOZf/ptMoX4+IZngq0TCHIqkoiAjQ0dvfN8QHjfHWmgRPCAx6hAeEagsric52lG0yzztklD9oEKGOthAc9BVX3kuB38NDfI2d/M69qyEsT7+8Zu+Ky4kBbCZ0Zk8m3xiPfGMUD+0Q5Th2eQg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 3, 2026 at 1:40=E2=80=AFPM Piotr Jaroszynski wrote: > > On Mon, Mar 02, 2026 at 11:19:46PM -0800, James Houghton wrote: > > This is similar (sort of) to a HugeTLB page fault loop I stumbled upon > > a while ago[1]. (I wonder if there have been more cases like this.) > > I see that your commit 3c0696076aad ("arm64: mm: Always make sw-dirty > PTEs hw-dirty in pte_modify") from that discussion was picked up and > it's very relevant for the hugetlb exposure question. With your patch, > do we have a guarantee that sw-dirty implies hw-dirty in all cases? If > yes, then there should be no exposure for that path. But it still makes > sense to make it more explicit. At the time, I was unsure that the patch made it *impossible* for Linux to ever write sw-dirty hw-clean PTEs, but, after that patch, such a write would have to somehow avoid pte_modify(). That seems unlikely; that was satisfactory for me at the time. I thought (and still think) that explicitly fixing the HugeTLB path would be a good idea. I think that patch wasn't taken because it wasn't necessary to fix the bug I was staring at. So if you want to take the patch to the HugeTLB path[2] or improve it in a v2 here, please do! Thanks! [2] https://lore.kernel.org/all/20231204172646.2541916-2-jthoughton@google.= com/ > > [1] https://lore.kernel.org/all/20231204172646.2541916-1-jthoughton@goo= gle.com