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([36.28.158.221]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-841d70f1ed8sm828385b3a.43.2026.05.26.20.56.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 May 2026 20:56:31 -0700 (PDT) From: Xueyuan chen To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 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, hpa@zytor.com, david@kernel.org, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, ryan.roberts@arm.com, dev.jain@arm.com, lance.yang@linux.dev, yang@os.amperecomputing.com, jannh@google.com, Xueyuan Chen Subject: [RFC PATCH 2/3] arm64/mm: make huge zero folio read-only in linear map Date: Wed, 27 May 2026 11:56:06 +0800 Message-ID: <20260527035607.14919-3-xueyuan.chen21@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260527035607.14919-1-xueyuan.chen21@gmail.com> References: <20260527035607.14919-1-xueyuan.chen21@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Xueyuan Chen Implement arch_make_huge_zero_folio_readonly() for arm64. Once allocated, try to make the folio read-only in the linear map so unexpected writes fault instead of corrupting shared zero contents. Respect can_set_direct_map() before touching the linear map, and treat the pageattr update as best effort: it can still fail while splitting a leaf mapping or applying new permissions. If that happens, generic THP keeps using the writable persistent huge zero folio. Co-developed-by: Lance Yang Signed-off-by: Lance Yang Signed-off-by: Xueyuan Chen --- arch/arm64/Kconfig | 1 + arch/arm64/mm/pageattr.c | 16 ++++++++++++++++ 2 files changed, 17 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index fe60738e5943..3cd705dd5251 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -44,6 +44,7 @@ config ARM64 select ARCH_HAS_PREEMPT_LAZY select ARCH_HAS_PTDUMP select ARCH_HAS_PTE_SPECIAL + select ARCH_HAS_READONLY_HUGE_ZERO_FOLIO select ARCH_HAS_HW_PTE_YOUNG select ARCH_HAS_SETUP_DMA_OPS select ARCH_HAS_SET_DIRECT_MAP diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index ce035e1b4eaf..51ce31e74a18 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -3,7 +3,9 @@ * Copyright (c) 2014, The Linux Foundation. All rights reserved. */ #include +#include #include +#include #include #include #include @@ -147,6 +149,20 @@ static int __change_memory_common(unsigned long start, unsigned long size, return ret; } +#ifdef CONFIG_READONLY_HUGE_ZERO_FOLIO +bool __init arch_make_huge_zero_folio_readonly(struct folio *folio) +{ + unsigned long addr = (unsigned long)folio_address(folio); + + if (!can_set_direct_map()) + return false; + + return !__change_memory_common(addr, PMD_SIZE, + __pgprot(PTE_RDONLY), + __pgprot(PTE_WRITE)); +} +#endif + static int change_memory_common(unsigned long addr, int numpages, pgprot_t set_mask, pgprot_t clear_mask) { -- 2.47.3