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b=kwZ4Y3EAFDceBci5/+JDost4FCO6v6ExEQloPZiqRWJa6DrOpq59BDlANcRZ5W9Da 0YkGiIrhMIM0Y4oA3bJVAPkVAkMh2ZDVas7JYI4vB/gxTsPFEuUMoap5+zn8l201ss vIrebluu5TiTYiThICUXUVwuBhTr2+8j6uG17pIcaC1Lj4tVaIfDE0cv0ER0HX98uz BePxSlC+haHMQiO2On7vvkPHUFeyRxeSZw75yBTaFsekJcP5eIqD1cV86KrTa3gu2b J4NCub9aTVDwfl0AlDdoa8TdACemyKWz1brmqYF2P1K9hN4ToS6wnUkW4CYRGUNcuN N3/1cVUgAH0IQ== Date: Mon, 7 Sep 2026 17:36:09 +0300 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Xueyuan Chen , akpm@linux-foundation.org, ljs@kernel.org, usama.arif@linux.dev, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, kas@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 1/3] mm: make persistent huge zero folio read-only Message-ID: References: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> <20260901151818.3191443-2-xueyuan.chen21@gmail.com> <69db9546-d14d-4107-96b7-30963292c2bd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <69db9546-d14d-4107-96b7-30963292c2bd@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1820D100003 X-Stat-Signature: cjef5xihq9jkppbb1aaajmwyb6gybcwc X-HE-Tag: 1788791781-90163 X-HE-Meta: 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 U23b7Rxh /6dvi/olzOSrfMAbNtx2hLShKA9omy/FK2l9ZceMejIuvjm/QLvGpKCtET6F+4TDHXTnEJ+uvhwYLhxGQ/oK3MW2BXs+LUzRWZ52d2KAZ0Ts3BUwX16lX8+qgCRY3NANarJq4CbvU4MVwPt+yjF6EoGtzeoJu7etI2UsqzIIl1G67VSEHtDO0g90HCyciif7NAAKJyRqxqqOAU/uXtyBQS2F6pCv+F8Divw28QbQ9hhsZYMV52wn1PFMggpS+MtRcue20Yjj4w7OXLgLsnrh7LoR3Js9fFzx/W/QGzkvEX30HO3Xz19abzM3yjAmu5DqIcTUT+bGBOzp1nH1bwsk7aLNCvFhPqQ03kol9eBuXk9Exdxc5vLgId9LDsw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 07, 2026 at 01:18:42PM +0200, David Hildenbrand (Arm) wrote: > On 9/7/26 08:03, Mike Rapoport wrote: > > Hi Xueyuan, > > > > On Mon, Sep 07, 2026 at 09:11:14AM +0800, Xueyuan Chen wrote: > >> On Sun, Sep 6, 2026 at 6:00 PM Mike Rapoport wrote: > >>> > >>> > >>> I believe this is an historical artifact. change_memory_common() already > >>> updates the linear map when a vmalloc mapping switches to RO and the system > >>> supports it. > >> > >> On x86, set_memory_ro() does work on direct-map addresses. > >> > >>> > >>> I believe arm64::set_memory_ro() can change the linear map in the general > >>> case as well as long as can_set_direct_map() is true. > >>> > >> > >> On arm64, I'm reading arch/arm64/mm/pageattr.c, and the linear-map > >> update in change_memory_common() is only reachable for vmalloc > >> addresses: > >> > >> set_memory_ro > >> change_memory_common > >> area = find_vm_area((void *)addr); > >> if (!area || ...) > >> return -EINVAL; > >> > >> So set_memory_ro() on a linear-map address returns -EINVAL on arm64. > > > > And I believe this is an historical artifact rather than necessity. For > > configurations that allow set_direct_map on arm64, change_memory_common can > > update direct map too, it just need to be implemented there. > > > > Are we sure the other architectures do what we want in their set_memory_ro? It's a zoo right now :( Although most of them do. But we need to sort it out anyway because of increasingly growing demand for modifications of the kernel page tables. I started something here: https://lore.kernel.org/linux-mm/20260721-generic-set-memory-v0-1-v1-0-2c1fc62306b3@kernel.org/ Now that x86 CPA is nearly fixed, I can look into the next iteration. > Having a dedicated set_direct_map_ro() with clear (documented ;)) semantics does > not sound too crazy to me. It's not too crazy, no. Still making arm64 more aligned with x86 and other arches that update the direct/linear map in the set_memory_ro() seem a good thing on it's own. > -- > Cheers, > > David -- Sincerely yours, Mike.