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b=QIPJIqcnFHP0Lub1MpXj6uRKUv0FSKOwY+sKSOczIkurDFVg8DJ/zw7OLg5EB1ma2 4f0nD1HaGoa20C0MK76SEYuvFrXMDliytjO0IYEiTMoFIOq+M5I138pybc42UHA94d FOCqIBC6kJ76AIN2jWAkgAIjdaufr79vdXXUWUzVc+bl6XxXw5qNChplpmxaw0oQIt 64JewSBIMk61QWyocXlPGeqiA5+54lMnNUrXjwqq2CMadvw+trfiqKrzs+JZxbVx1D czt5lT+NJ/uSVNKO9dDRZFe50OVsDUXIcboFdDYOzOx2mjo5h5nLUzUCYAY0hL7gnx asXnfjRtMbFSw== Date: Mon, 7 Sep 2026 09:03:22 +0300 From: Mike Rapoport To: Xueyuan Chen Cc: akpm@linux-foundation.org, david@kernel.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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0CE671A0003 X-Stat-Signature: huyn38k15jg4biszu768bnagj87rg8pg X-HE-Tag: 1788761016-36385 X-HE-Meta: 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 BKiLHPhB RG2Z5lq+afZzEnpZXE/K+gNphuLHLT91HDOJjyRKSLPoSKMWsDlR91PmJyGwPQc8+XNJFXm7njozKm51FFGAV5Zv0sDeesvwAkHevPfP/Rv8rSd4zXBjQ6QwAtH6RPOEYxU4n2FaFe71xmYtMrw+VoWF0BRCtOu0/aTEAeAGWY+Y6IQkAQkZ/rTm+Qnhz1g2MZTlehcqsj4hHm+ZFMsoKMtWEys5dDrp9Xx6UGkaTuUbrn9EGpV8a0AGQ9eU1JYnRf/CXdZzaJHGqM3SwOtGhM5hslTLOJ7E9fsCCMk6EaIXEfXX9MqJCJsH5tgvUf9I6wk7mdvUwfR/efeavILLvWQEOooqpMjHiSZSNY9Iw4dNioT/e5XpwgRuJdQoTUE7VQ2R6 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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: > > > > > > > + > > > > > + /* Highmem folios have no permanent direct-map mapping to protect. */ > > > > > + if (!folio_test_highmem(huge_zero_folio)) > > > > > + set_direct_map_ro(folio_page(huge_zero_folio, 0), HPAGE_PMD_NR); > > > > > > > > Sorry, I don't remember if it was discussed previously, but why can't we > > > > use the existing set_memory_ro() here? > > > > > > Hi Mike, > > > > > > We want to change the linear map here, but arm64 set_memory_ro() only > > > works on vmalloc addresses. > > > > 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. -- Sincerely yours, Mike.