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Wed, 22 Oct 2025 15:08:10 -0700 (PDT) Received: from localhost ([2a03:2880:25ff:4::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-785cd4584casm1358607b3.0.2025.10.22.15.08.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Oct 2025 15:08:09 -0700 (PDT) From: Usama Arif To: dwmw@amazon.co.uk, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, ardb@kernel.org, hpa@zytor.com Cc: x86@kernel.org, apopple@nvidia.com, thuth@redhat.com, nik.borisov@suse.com, kas@kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, kernel-team@meta.com, Usama Arif , Michael van der Westhuizen , Tobias Fleig Subject: [PATCH 0/3] x86: Fix kexec 5-level to 4-level paging transition Date: Wed, 22 Oct 2025 23:06:24 +0100 Message-ID: <20251022220755.1026144-1-usamaarif642@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This series addresses critical bugs in the kexec path when transitioning from a kernel using 5-level page tables to one using 4-level page tables. The root cause is improper handling of PGD entry value during the page level transition. Specifically p4d value is masked with PAGE_MASK instead of PTE_PFN_MASK, failing to account for high-order software bits like _PAGE_BIT_NOPTISHADOW (bit 58). When bit 58 (_PAGE_BIT_NOPTISHADOW) is set in the source kernel, the target 4-level kernel doesn't recognize it and fails to mask it properly, leading to kexec failure. This series fixes the issue in three parts: Patch 1: Fixes the x86 boot compressed code path by replacing direct CR3 dereferencing with read_cr3_pa() and using PTE_PFN_MASK instead of PAGE_MASK. Patch 2: Applies the same fix to the EFI stub code path. (Done in a separate patch as Fixes tag is different). Patch 3: Moves _PAGE_BIT_NOPTISHADOW from bit 58 (_PAGE_BIT_SOFTW5) to bit 9 (_PAGE_BIT_SOFTW1), which is already properly masked by older kernels. This provides backward compatibility without requiring patches 1 and 2 to be applied to all existing kernel versions, which is not feasible for production systems or live patching. Co-developed-by: Kiryl Shutsemau Signed-off-by: Kiryl Shutsemau Signed-off-by: Usama Arif Reported-by: Michael van der Westhuizen Reported-by: Tobias Fleig The patches are based on aaa9c3550b60d6259d6ea8b1175ade8d1242444e (next-20251022) Usama Arif (3): x86/boot: Fix page table access in 5-level to 4-level paging transition efi/libstub: Fix page table access in 5-level to 4-level paging transition x86/mm: Move _PAGE_BIT_NOPTISHADOW from bit 58 to bit 9 arch/x86/boot/compressed/pgtable_64.c | 8 +++++--- arch/x86/include/asm/pgtable_types.h | 4 ++-- drivers/firmware/efi/libstub/x86-5lvl.c | 5 ++++- 3 files changed, 11 insertions(+), 6 deletions(-) -- 2.47.3