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b=kt9KYkEsCfbD9dm+VVTaprLzLusq2rWJ2jIynnLBJ2bx410RackA+uvvuDGzpnxdn NAxeKAd3r6AxY2P3hP+9EMKM5GLj3cuURDA8cswfqP0XczAW0XG4zULfNmCyENAwhW pD1sxAG9oH4B/qtvnpENoP49KBCym1taieSCDgrs2Kcca8oVO7rxnWGUJJmEj5WDjP RRDagBX+jz/ZKYQrI40wjff7hBOs04j3xebzbOL78NtIkU2zwO/lmZojcd/M+Yz2B5 xXZ8udJtB3+hI0wUtz6BdqD3nG06QmCLAN4ZnkCVaIVEvPF0um4PAHD7yVDlgGMFeG IZBb8K21oKtRw== Message-ID: <2e8dae0b-d81e-4c5d-b4d5-c80bde07a314@kernel.org> Date: Mon, 7 Sep 2026 16:48:01 +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 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 References: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> <20260901151818.3191443-2-xueyuan.chen21@gmail.com> <69db9546-d14d-4107-96b7-30963292c2bd@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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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 :( Yeah, that's why I'm asking :) > 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. The question really is whether we want to use a single interface for all page tables. I quite like a page-based directmap interface. Other page table areas are not necessarily page-based. It also expresses which types of operations we expect on the direct map. One could, of course, use set_memory_ro() internally to implement set_direct_map_ro() (and similarly for other variants); but at least set_direct_map_*() would have clear, well documented semantics. > > 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. Right, but I'd much rather user set_memory_ro() later to implement set_direct_map_ro() [initially on architectures where we made sure that it actually does what we expect? later maybe generically] -- Cheers, David