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b=V7H57MqPiRK07WRpuk61WJMDO1K3Rp4f7+L6YDzJ11J38aG0GqD3Af0XJwNQCEP2D Nmulu89ZObRsODv3lW3/zKxIbl2tSLzSYsr0XsZiUQxpZiNkSNiQGByWkGMnQc3zwz tANAXBCIcRDhJg77kAG3epLL1OxYtgvDdBY88kEoUxhUd6YVRymuBDB9jyOClheQHY Ps7P9rRmBnum+lYJSLjz+BER+uTypXkZhcLbVuGFoVSWp1CMUBZIBDj98+VHVlsWrZ r6rIUGdiOlWGE0+pVR0gOPKFdNfuQw7CvoOuEKV7k67zvPbYqifgfed/rRZKyJJ4Fq cUw3KDN/P3lJQ== Message-ID: Date: Fri, 19 Jun 2026 13:09:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 1/3] mm/huge_memory: make persistent huge zero folio read-only To: Xueyuan Chen Cc: dave.hansen@intel.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, catalin.marinas@arm.com, will@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, hpa@zytor.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, yang@os.amperecomputing.com, jannh@google.com References: <0e5b23a6-4895-454a-9dfa-6dc21adc2991@kernel.org> <20260619025553.226940-1-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: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: F379D40005 X-Stat-Signature: p7ifj3j1151dz1f1xgewfzsfjfewygij X-HE-Tag: 1781867358-562787 X-HE-Meta: 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 A7fzLLWg w3BqZgTLT6JO1RkVkMtNjEi8zJdYloeI5UxAzDiKc2HoYj6IxMHqXMhTYhOp8E/Z7Xdh/XCf2u+ZW/Whjv90uVYR7WPzuJ8leXPCptp/264DBybA7+fmr6/o/ovx83iTwoc3tf1ENPKkRRm+eEu7Hs1NVqPHbYQsEvgMVNC1pJrmnLKWj8ngRUp85x3mtvC3BEbkBvJ9VAUq530EDx9R4oQ+kt7H6yVRXzx6xi2A2/OgzielELieklQlzJGd/tdWWQiIfE64esQAell2qvYYnlW+7JLnGHDRZa97Ygkj7bCVOuhf65LVt+0RHyxMHSf1SFZ2qAnKJulbhIvCs4E5OVBPptoSEVUwyfea3Z8fCg9CjF9HC4A2cBAe2GKdjxYxSwUfZvEHJTQFk2ZZ8ziDfJjKYq9+XmLIs1VuZisfloXGe8lM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/19/26 04:55, Xueyuan Chen wrote: > On Thu, Jun 18, 2026 at 02:36:25PM +0200, David Hildenbrand (Arm) wrote: > > Hi, David > > [...] > >> Best to wait for some feedback. > > Sure. > >> I do wonder whether we want to pass an address instead of a page. >> >> https://lore.kernel.org/r/20260410151746.61150-2-kalyazin@amazon.com >> >> Wants to convert existing ones as well. >> >> That would imply that the caller must check for highmem. >> >> But then, we could just use existing set_memory_ro(), right? >> > > Agreed. Passing an address and reusing the existing set_memory_ro() > definitely makes things simpler. > > However, there is an arm64 specific limitation: > currently, the set_memory_r* api on arm64 only support the vmap > region and do not handle linear map addresses. > > If we go this route, should I extend the arm64 set_memory_r* > implementation in the next version? The plan would be to make it check > for the bblm2 feature and modify the linear map PTEs accordingly. > What do you think? Good point! It's not really clear on which ranges set_memory*() is supposed to work ... arm64 only works on vmalloc/vmap, x86 and riscv on ordinary directmap ... what a mess. Having a new direct-map specific function with clear semantics might indeed avoid even messing with that. So, yeah, given that we have set_direct_map_invalid_noflush set_direct_map_default_noflush set_direct_map_valid_noflush Let's add a set_direct_map_ro() Or (my preference) change_direct_map_ro() But given the existing naming scheme ... maybe just set_direct_map_ro() and we'll clean this up another day. Now, should there also be a "_noflush" in there, or who is supposed to flush the TLB (or don't we flush at all, because it's used early during boot so far)? In any case, for this function we should add excessive documentation and define clear semantics. -- Cheers, David