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b=MBQBoKupOvPboBHAGShCa2KQHrEqsjR/MrgjtQuP2sCUGgdjYOu9EegxmvwTqeS0A BhyCWDRazJkTCdvKvi93Chg2Dt9yUC3zjnKvtF8cj2a4zGLqh5ZI6f8JR+LbqZAri9 pjdttV/hbpEzrBaTLLeHdF7nRVgYcdVsz67gdzy+qo+ccnK2foO3SKTNOayx62tWdr B0iw3aidemCTPsAIvkYeMn4HjnRBFXQ7HfWuv2F6iQ02aXFnU/W0VSqZm5u3ao3vNC Zh9tR/ItbPiOGYbq8CnVXm7Zb27eTS7lH4NUtCOpOAUjhch2Ric3mQEgBHXljExawj jywrQTpbflAcw== Message-ID: <1c0141e8-3033-4f59-b247-34dee14cbb1f@kernel.org> Date: Sun, 25 Oct 2026 13:34:13 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs To: Zhao Gongyi , catalin.marinas@arm.com, will@kernel.org, Ryan Roberts Cc: dev.jain@arm.com, baolin.wang@linux.alibaba.com, lance.yang@linux.dev, mark.rutland@arm.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261013093600.54995-1-zhaogongyi@bytedance.com> <3b57c214-6a43-4fc7-a531-fb5eac196465@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 188F4140009 X-Stat-Signature: upzuzajrczgmzhe7w75151s1rfrktwuq X-Rspam-User: X-Spam-Status: No, score=-6.5 required=3.0 tests=BAYES_00,DATE_IN_PAST_12_24, DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793007665-626640 X-HE-Meta: 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 qkELsy1V /Vid/4KWjcM40W4eUM/DYa5a2ugewzW1goSo49OgpaniMYmcxVVkfh0hvkkYDjVtRBHunIyKPmMgE3lrUpSHqpe+kuorpPpp9QEQ1oxIKpj1JckPQncfVjanWTnLXgh1OmDMquKL3KsHE70PsL5QnS/HcgBStkzM+7RcnYoBCZOyeXvZAXVPZr7p5OO39nhCb7YXJpiiTbI+z1EL32PSQOQTCxooB2RQcqv0Nzvel3tXovyJNuTLf3393LmeOHKd4B7QKrF4gIm99tfNY9MgofkLeivJnyrIZ1I+kap9CBIeMfe2tZ6QT2mF8xS1Jh97E8OyJtBq4H3dzFItQ3d7ClPVsiQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/24/26 18:00, Zhao Gongyi wrote: > On 10/24/26 4:55 AM, David Hildenbrand (Arm) wrote: >> >> Hi, >> >> sorry for the late reply. >> >> If we have the spare PTE bit, why shouldn't we just use it? >> >> It will make batching over PTEs faster. And we care about that for present PTEs. >> >> So I don't quite see why the stable fix couldn't just do it right away? Do you >> have a prototype that shows that it would require significant code changes? >> > > Hi David, > > I tried a small prototype that keeps PTE_CONT on present-invalid PTEs. > It leaves contpte_set_ptes() unchanged and makes contpte_try_unfold() > recognize pte_present(pte) && pte_cont(pte), instead of checking only > pte_valid_cont(pte). > > With this change, the guard-marker reproducer passed 100 iterations > in an arm64 QEMU/KVM guest running a KASAN-enabled kernel. The fork > and PMD-split probes passed five runs each, with no warnings or KASAN > reports. In the earlier A/B test, the unmodified kernel failed on the > first guard-marker iteration. > > The prototype makes the reported reproducer pass with a small change > while retaining PTE_CONT. I therefore cannot point to evidence that > fixing this failure requires significant code changes. Can you paste the code here for easy review if that it the right approach? -- Cheers, David