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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Pasha Tatashin , Russell King , Catalin Marinas , Will Deacon , Ryan Roberts , linux-arm-kernel@lists.infradead.org, Huacai Chen , loongarch@lists.linux.dev, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Gerald Schaefer , linux-s390@vger.kernel.org, "David S. Miller" , Andreas Larsson , sparclinux@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Ning Sun , x86@kernel.org, tboot-devel@lists.sourceforge.net, Ard Biesheuvel , Ilias Apalodimas , linux-efi@vger.kernel.org, Vishal Moola , Alistair Popple , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20260714-remove_pgtable_cdtor-v1-0-44be8a7685d7@arm.com> <20260714-remove_pgtable_cdtor-v1-17-44be8a7685d7@arm.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260714-remove_pgtable_cdtor-v1-17-44be8a7685d7@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 14/07/2026 16:04, Kevin Brodsky wrote: > Commit 8b1cb4a2e819 ("mm/pagewalk: fix EFI_PGT_DUMP of > espfix area") made no-VMA page table walks use > pte_offset_kernel() for any address above TASK_SIZE. This avoided > pte_offset_map() validation on EFI page table dumps, where efi_mm > could walk x86 espfix PMDs that intentionally look bad to pmd_bad(). Sashiko rightly doesn't like this patch. Turns out 8b1cb4a2e819's commit message and the comment it added are narrower than what the problem really is: on x86, due to things like /sys/kernel/debug/page_tables/current_kernel, we may be walking kernel page tables even when walk->mm is a regular user mm. Just checking the mm is therefore not sufficient. Will replace this patch with a rewording of the comment to avoid suggesting the issue is specific to efi_mm. - Kevin > efi_mm is now marked with MMF_KERNEL, and no-VMA walks use > mm_is_kernel() to select pte_offset_kernel() for kernel mm's. As a > result we no longer need to handle the EFI_PGT_DUMP case explicitly.The > address check is therefore redundant for EFI_PGT_DUMP and makes the > condition harder to reason about. > > Remove the address check and associated comment; mm_is_kernel() > should be sufficient on its own. > > Tested by booting x86 QEMU with CONFIG_EFI_PGT_DUMP=y and reading > /sys/kernel/debug/page_tables/efi. > > Assisted-by: Codex:GPT-5.5 > Signed-off-by: Kevin Brodsky > --- > mm/pagewalk.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index a3f47d1de3c5..0dd9d4ad9b68 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -68,17 +68,14 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, > if (walk->no_vma) { > /* > * pte_offset_map() might apply user-specific validation. > - * Indeed, on x86_64 the pmd entries set up by init_espfix_ap() > - * fit its pmd_bad() check (_PAGE_NX set and _PAGE_RW clear), > - * and CONFIG_EFI_PGT_DUMP efi_mm goes so far as to walk them. > */ > - if (mm_is_kernel(walk->mm) || addr >= TASK_SIZE) > + if (mm_is_kernel(walk->mm)) > pte = pte_offset_kernel(pmd, addr); > else > pte = pte_offset_map(pmd, addr); > if (pte) { > err = walk_pte_range_inner(pte, addr, end, walk); > - if (!mm_is_kernel(walk->mm) && addr < TASK_SIZE) > + if (!mm_is_kernel(walk->mm)) > pte_unmap(pte); > } > } else { >