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b=F8m423LhiG/t/9Wa6UuLgMPisSPSaM0ws6sLzcdYwfW2FEYdK/K+Z5A9zDpAI0e7z 7zcW1KROfscWEZhgA/J8JMfiW9sSjf23XIOE1DtFpqV6RhSBlXktdEsVQQTJgaOMM4 U+NDNAEYwpedUUzpWNcWoZO3jLmIdBS4eK85R8SBGtCl4vMw4N9c0Nuc0u/AMBroJV oRiUG+v7J4tZ82zGGs47AX3GVu31zIt3DwoR5PgXBUt3YEZASX0JDS1IsnET4tQ56d O1HMQB9Is+Yp9B8WSFxR5SaTnXfE7G6ZgJ+Now4boANlh1gpw9obeOJHtK/TEdEkGs kj3KDL5gjdRFA== Message-ID: <69db9546-d14d-4107-96b7-30963292c2bd@kernel.org> Date: Mon, 7 Sep 2026 13:18:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 1/3] mm: make persistent huge zero folio read-only To: Mike Rapoport , Xueyuan Chen Cc: 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 References: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> <20260901151818.3191443-2-xueyuan.chen21@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: EE51540002 X-Stat-Signature: wksboqzno3dftgwbqzjmq1cjodm1k5ph X-HE-Tag: 1788779931-963969 X-HE-Meta: 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 AoLN9vnF Yi8SatuUiweCP9/Qjq+uWgx1CVgg/jinTCflKcjbIynoTqL9NE3ZZytvXlYuri6zkDZYp2rNRhWJIYkHHFbbHHkBrYoI8K5D0DAit79vST2mLA72Mmz9n1Jmq813maI4BnfEFb/nuJ0gTt5AmhEkGdxlfyKx4nEeUk11J+ZayBzBGWE6IhnLWPmeTGSpptIGpYzW2sYexsI7zR1SpJxt8W4WXMUAl5KakRll0nQFYzAL2gBrfJBKc7A6Zr9ZM3K5uog44KIYYditrPrv/h9/ZuKnUQI32msACrnEHJcmecFYgEwM+YxMeINV2UV0Dj4Ldwg5XccLVVujL1qFPO0kREL11NyhPcQ9WfOUYRjTwOcn6iFmKj7u0EcLBMmXQ1+j71dWZ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? Having a dedicated set_direct_map_ro() with clear (documented ;)) semantics does not sound too crazy to me. -- Cheers, David