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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FqQCx48UJNUfeHogU9/y9HwEqlbbhAQ6HAGisLpAoZ06/5JM87N/K8zIXSOkQS9Lo tzFVemZDjh6FMqDs/3oBIzs/gxTzjo2BY91OzyLW22GOwYSGCjWr8ywmF0OCMoI9D1 02im7RrlbLfHvqkoRtrjjP2YXspf26q5PHLafXU8= Message-ID: <8fdbe0d6-87fd-441c-b6d2-baac380f6fb3@arm.com> Date: Sun, 5 Jul 2026 13:38:41 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/6] arm64: make huge_ptep_get handled unaligned addresses To: Andrew Morton Cc: muchun.song@linux.dev, osalvador@suse.de, ljs@kernel.org, david@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> Content-Language: en-US From: Dev Jain In-Reply-To: <20260705003559.8b124d2b94b685cc2e4e77ae@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 735F41A0006 X-Stat-Signature: k3pe7t73u5p99p4wwitpjqkqswuks5n8 X-HE-Tag: 1783238936-796685 X-HE-Meta: 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 ljG3snDy Q553n3vRQpuBMWUG3ABPiTtJAKmg28xVQ+CUUipi1kcxD6t1x6zJo9EW/gVLu4HqgESVb1BgY74KCf1/bE3FsRNw3NtLPAOLx14GSjJ9bp8SxFNQqx5IkhRuVgsytY26wz9qxm72lDqp0j1UO0S0uCforr5DvojS8XTBDIf/IDW3/GCa/TPrZHZJsqCwn/G3ZPDqfutQRE7iip6ZOIlpVcv9LmYZfXT5bu7HoQPJxXXjhKOXspE0hPItWLyVLUS3fQt8j/MqOwttvtZXqMkAVdE5AIq4GyoGW5gtJ5BDdYzxdJJKWdiyIx072azjEaLZVt1GshnA7UCcAA9wBYLgJE1t/6aNSXqi8Jw97qfo/cu/DJrK7fpy39y3HHt5H433NE3tQpYmM8ok8zqozMgKu6N8CgQAK7RPswQsw0qu/ZM9OymxmBDHh1nUCRICX1fTZXH94 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. >