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[2a02:3100:a16a:7801:fd8c:4b37:36b4:e53a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49b926874fdsm356104405e9.4.2026.09.01.06.18.27 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 01 Sep 2026 06:18:27 -0700 (PDT) From: Karl Mehltretter To: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org Cc: Karl Mehltretter , Anshuman Khandual , Ryan Roberts , Mark Rutland , Andrew Morton , Muchun Song , Oscar Salvador , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] arm64: hugetlb: fix BBM for mprotect() on contiguous PTEs Date: Tue, 1 Sep 2026 15:18:23 +0200 Message-Id: <20260901131823.15799-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit huge_ptep_modify_prot_start() clears a hugetlb entry before changing its permissions. For contiguous PTE mappings, break-before-make (BBM) requires a TLB invalidation after clearing the set and before making any entry valid again. Commit fb396bb459c1 ("arm64/hugetlb: Drop TLB flush from get_clear_flush()") removed this invalidation, relying on the deferred flush from the core code. Commit 410982303772 ("arm64: hugetlb: Restore TLB invalidation for BBM on contiguous ptes") restored it for huge_ptep_set_{access_flags,wrprotect}(), since a deferred flush is too late for the break step. The modify-prot path has the same problem. Use huge_ptep_clear_flush() for contiguous entries so that the TLB is invalidated during the break step. Leave huge_ptep_get_and_clear() unchanged because it is also used by teardown paths, where the deferred flush is sufficient. Fixes: fb396bb459c1 ("arm64/hugetlb: Drop TLB flush from get_clear_flush()") Assisted-by: LLM Signed-off-by: Karl Mehltretter --- An instrumented QEMU detected the missing break-step TLBI on an unpatched kernel and none with this change. A fork() control exercising huge_ptep_set_wrprotect() remained clean. No user-visible failure was reproduced. The QEMU checker was exercised with 4K and 64K base-page kernels. The patched kernel passed the LTP hugetlb tests with both -cpu max and -cpu cortex-a72 (16 TPASS and no failures). Testing on Neoverse N1 hardware would be welcome, as it can use the contiguous hint and can be configured to report TLB conflicts. arch/arm64/mm/hugetlbpage.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index 8e799c1fe0aa..bb53a04b73b2 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -517,6 +517,11 @@ bool __init arch_hugetlb_valid_size(unsigned long size) pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep) { unsigned long psize = huge_page_size(hstate_vma(vma)); + pte_t pte = __ptep_get(ptep); + + /* The break step for contiguous PTEs must include the TLB flush. */ + if (pte_cont(pte)) + return huge_ptep_clear_flush(vma, addr, ptep); if (alternative_has_cap_unlikely(ARM64_WORKAROUND_2645198)) { /* @@ -524,7 +529,7 @@ pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr * when the permission changes from executable to non-executable * in cases where cpu is affected with errata #2645198. */ - if (pte_user_exec(__ptep_get(ptep))) + if (pte_user_exec(pte)) return huge_ptep_clear_flush(vma, addr, ptep); } return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep, psize); base-commit: 786262be6048deab760f68c8acc2c85607165894 -- 2.53.0