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b=VoNyyimYnqqKLu1tQ9fTHSAp21AMnYBuiWyDfCJxhaM5/Kel8HyLFCw14x1s78N9U 7mGtgGN7PQ4XmdHlIMaW/7mlNyN/cMHkDlR8PbVdbyty6JdKay20g0qf+oHdS6g7BD uF9eg8bFVbc42WPLvi/yhsVBGSO6LkgMOTX2l+QzthLuq25fpiD6WwgLlbBL/WWC2U kdApDETEjy1WcUFc6A2sdKhZdnKGL20lVZikzBik4ow8GBgILpM6f0eCBgmOBqBrF4 hqE4J+OoveSZBRXmoWaSnTu/fspZaLo9MMP1OudEZa2PkV/QKRUvIlQW0v+WLjL8KI c0u/RfKS2F/2g== Message-ID: <4b4e8007-3747-457a-85cc-d1003e1c8fe2@kernel.org> Date: Mon, 6 Jul 2026 10:45:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/6] arm64: make huge_ptep_get handled unaligned addresses To: Dev Jain , Andrew Morton Cc: muchun.song@linux.dev, osalvador@suse.de, ljs@kernel.org, liam@infradead.org, riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, apopple@nvidia.com, rcampbell@nvidia.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, ak@linux.intel.com, nao.horiguchi@gmail.com, mel@csn.ul.ie, j-nomura@ce.jp.nec.com, pfalcato@suse.de, tglx@kernel.org, dave.hansen@intel.com, jpoimboe@kernel.org, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20260703114202.365553-1-dev.jain@arm.com> <20260703114202.365553-2-dev.jain@arm.com> <20260705003559.8b124d2b94b685cc2e4e77ae@linux-foundation.org> <8fdbe0d6-87fd-441c-b6d2-baac380f6fb3@arm.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: rspam06 X-Rspamd-Queue-Id: 28B3D180004 X-Stat-Signature: o4c1uiqfcohewxdy1u678u641z9y6px8 X-Rspam-User: X-HE-Tag: 1783327558-349584 X-HE-Meta: U2FsdGVkX1+1AqtKF347XEo2ybZh4ULFWPpkHwPod13zRG+iJTUFECHJ97PdKv1o8+ZePikcZJMP92E3s26M0tPDd4agXf1mdi0DG+mUGALHmloXG7tOpIgajpYBQ2+VuuM2xl8M78BGaOLMPaVdskj9o+/tkvlEcgwRDDzw9lVxHfUT59oOgrGuLwzwVw5sYOQyGwNFtgJbC5vqCqKkBW3eW0LnC7zeIavF6wbtrZMCzpmKEgFx4gFj5+TE+ECSzRlJN/+1RxjydYZ0kh0LLELetN/X8oSCG2pTmBs6AGx6OcAvvx2BKVcahzjoBRy/6EphmwpO55CamutKhOXrH0Gh7bnX2linkIoob3USPO35Oeruyv0rpGRKxrd5b54+VbG2kvQrlTsUjhIxOAze0ZQoarcLSjeVWIwC1zJBIgCjPB4vRyqLBSvvGCJybFA3KksLIKeiafRysgd0CfLH93IIDbMiYM03WjphHaBN8t1or1Ydq/d1h/HQuZ/ApRRRRGhaT10XNl2PJEY7RR29Tt6MYtZVS23YN5S1IqhCT0wLQsKp+RSobJxQXdlfNXYndpNZtoUGspJJCHSLx6AOKdBVjOPRk+cQkMSHk1vPenFTw8mpgFsyjTLQze2mT9d9QMh5QSCzt7JLtKvgYczaVev5QwoqzkfGykPl68oCiNMmoYLEtYKDBuF5UCjMNSfwZHvXdDCumkHbq6GeEMABETDNghYKFJmZarUzf/KAjMjICOQt7zx3nflBGOMI2D9MUQP8RQy3yfnhp5mjzahwlzdHDXpJwQ8XCf01UTTTvqka+SsWhsBXEL3xLfN2LO0QvjUDQ8QKFx67Sb64QvsHhgI6JHshHN9uQvufzNnQ0+DvcC9wujI+zYWvcCcl1NYdtLARujNorjXeof+l1KgKQI+GxtPwNFR2ykaSgVK8tNuQXxnXW7mFIgmf5qiyHwcQQeizGtMykugPraubiAq EOqkb87o tE9XnpJQllOypx74R9Kt+sT+ywX5ip5U1b5JeMRz3gtgmTwApBzipUjKUznYoAJbtIz60dtfFhwIvATeH9UHjAB+RZKqE0C7qLQJXYKPjk73ligkjedkZJ7Tt6om0ObaH4LXTmcgGdyuNBCrDO8vtbG3DT4P6YbGtmTZNt6VQ3u4Yw1+q+5L6y11NGld6SklU6VhbTlJlPDQ5OmJuayA2xybcml4v+cjHXkZgztCmOPGmR5pG9SC/1FppGNZF6Cc26ixS7dZBEZGNaaHcHZofAEK+h5kX85f7h655t3FZaC0RTvHccMrwFAg5fL1vE/FILO1yg7U+1E//+ZKgvkXYHQIT47KJuMFH4jkK51/16/Gma1dV21yqrM5Ghffo7POSysrCpWftvGzZ7UWMX7Sps6DQrMhlvpHBNlsC/bB10M2ZD6NjB/SFRfacPI4YK8BUnAFfCXzZFqNsHCH7X3QBjHbRzw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/5/26 10:08, Dev Jain wrote: > > > On 05/07/26 1:05 pm, Andrew Morton wrote: >> On Fri, 3 Jul 2026 11:41:54 +0000 Dev Jain wrote: >> >>> huge_ptep_get() can be handed a virtual address pointing to the middle of >>> a contpmd/contpte mapped hugetlb folio (examples of callers are >>> pagemap_hugetlb_range, page_mapped_in_vma). >>> >>> The arm64 helper rewalks the pgtables in find_num_contig to answer whether >>> the huge pte we have maps a contpmd or a contpte hugetlb folio, and >>> returns CONT_PMDS or CONT_PTES, so that it can collect a/d bits over the >>> contiguous ptes. We can falsely return CONT_PTES instead of CONT_PMDS >>> if the addr is not aligned. >>> >>> Fix this by aligning the pmdp pointer down to a contpmd base before >>> checking equality with the passed huge pte pointer, to correctly answer >>> whether the huge pte is the base of a contpmd block. >>> >>> Fixes: 29cb80519689 ("arm64: hugetlb: Cleanup huge_pte size discovery mechanisms") >>> Cc: stable@vger.kernel.org >> >> Please describe the userspace-visible effects of bugs when fixing them. >> Particularly when cc:stable is proposed. Thanks. > > Forgot for this one. It should be, on systems where CONT_PTES != CONT_PMDS > (meaning page size is 16K) we could collect excess a/d bit state, meaning > extra work for the kernel. Even worse, right? We could walk 128 entries, when we really should just walk 16 (IIRC) entries, possibly reading garbage or even worse, into a memory hole at the end of memory? -- Cheers, David