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Mon, 30 Jun 2025 12:07:47 -0700 (PDT) Received: from localhost ([2a00:79e0:9d:4:efbc:81c2:63ca:f4bd]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-453a85b3211sm171495e9.1.2025.06.30.12.07.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Jun 2025 12:07:46 -0700 (PDT) From: Jann Horn Date: Mon, 30 Jun 2025 21:07:34 +0200 Subject: [PATCH] x86/mm: Disable hugetlb page table sharing on non-PAE 32-bit Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250630-x86-2level-hugetlb-v1-1-077cd53d8255@google.com> X-B4-Tracking: v=1; b=H4sIAHXgYmgC/x3MQQqAIBBG4avErBsww4iuEi2yfm1AKrQiiO6et PwW7z2UEAWJuuKhiEuSbGtGVRY0LePqwTJnk1baqKZWfLcN64ALgZfT4wiWbTW3DlYbM4FyuEc 4uf9pP7zvB5jCzAFkAAAA X-Change-ID: 20250630-x86-2level-hugetlb-b1d8feb255ce To: Dave Hansen , Andy Lutomirski , Peter Zijlstra Cc: Muchun Song , Oscar Salvador , Vitaly Chikunov , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Jann Horn X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1751310463; l=1751; i=jannh@google.com; s=20240730; h=from:subject:message-id; bh=fZfTk5Vh6fk3qEeQcDy4mPHUEYnCIWWCDffCZM4Mbko=; b=kvQS4ouJ3b19TCoh5GA7p1y72qr1wSvm2vBPrDtuH/ptozufVWlQnwIJEVJgZVGCD4avNN+Ph sdoHh9GDeRFB/3o80OYgEquVoPd1SnKDwWdYKGd/UzJKzG59yxQgeHs X-Developer-Key: i=jannh@google.com; a=ed25519; pk=AljNtGOzXeF6khBXDJVVvwSEkVDGnnZZYqfWhP1V+C8= Only select ARCH_WANT_HUGE_PMD_SHARE if hugetlb page table sharing is actually possible; page table sharing requires at least three levels, because it involves shared references to PMD tables. Having ARCH_WANT_HUGE_PMD_SHARE enabled on non-PAE 32-bit X86 (which has 2-level paging) became particularly problematic after commit 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count"), since that changes `struct ptdesc` such that the `pt_mm` (for PGDs) and the `pt_share_count` (for PMDs) share the same union storage - and with 2-level paging, PMDs are PGDs. (For comparison, arm64 also gates ARCH_WANT_HUGE_PMD_SHARE on the configuration of page tables such that it is never enabled with 2-level paging.) Reported-by: Vitaly Chikunov Closes: https://lore.kernel.org/r/srhpjxlqfna67blvma5frmy3aa@altlinux.org Fixes: cfe28c5d63d8 ("x86: mm: Remove x86 version of huge_pmd_share.") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Tested-by: Vitaly Chikunov --- arch/x86/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 71019b3b54ea..917f523b994b 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -147,7 +147,7 @@ config X86 select ARCH_WANTS_DYNAMIC_TASK_STRUCT select ARCH_WANTS_NO_INSTR select ARCH_WANT_GENERAL_HUGETLB - select ARCH_WANT_HUGE_PMD_SHARE + select ARCH_WANT_HUGE_PMD_SHARE if PGTABLE_LEVELS > 2 select ARCH_WANT_LD_ORPHAN_WARN select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP if X86_64 select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP if X86_64 --- base-commit: d0b3b7b22dfa1f4b515fd3a295b3fd958f9e81af change-id: 20250630-x86-2level-hugetlb-b1d8feb255ce --=20 Jann Horn