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Tue, 28 Oct 2025 03:57:32 -0700 (PDT) Received: from localhost ([2a03:2880:25ff:41::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-785ed196a0dsm26357697b3.27.2025.10.28.03.57.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Oct 2025 03:57:31 -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 v2 0/2] x86: Fix kexec 5-level to 4-level paging transition Date: Tue, 28 Oct 2025 10:55:55 +0000 Message-ID: <20251028105637.769470-1-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 PGD entry 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. 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). 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) v1 -> v2: - Remove patch 3 from v1 to fix kexec for source kernel in 5-level to 4-level transition where the 4 level kernel doesnt have patch 1 and 2 (Dave Hansen) - Add include for asm/pgtable.h to fix build for x86_64-allnoconfig (kernel test bot) - Use native_read_cr3_pa and for both paths (Ard Biesheuvel) Usama Arif (2): 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 arch/x86/boot/compressed/pgtable_64.c | 11 +++++++---- drivers/firmware/efi/libstub/x86-5lvl.c | 4 ++-- 2 files changed, 9 insertions(+), 6 deletions(-) -- 2.47.3