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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu Nov 5, 2026 at 7:03 AM EST, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > Zapping a range calls arch_check_zapped_pte() for every batch of PTEs, > which is every page for small folios, and arch_check_zapped_pmd() or > arch_check_zapped_pud() for every huge leaf. Only x86 implements them, as > out-of-line functions that warn about a shadow stack entry (Write=3D0, > Dirty=3D1) in a VMA without VM_SHADOW_STACK. > > The warning is a VM_WARN_ON_ONCE(), so without CONFIG_DEBUG_VM the > functions are empty, but the calls remain. With the SRSO "Safe RET" > mitigation the return of every such call mispredicts. > > The x86 helpers already keep such entries out of other VMAs. > pte_wrprotect(), pte_mkdirty(), pte_modify() and their PMD versions go > through SavedDirty, and only pte_mkwrite() and pmd_mkwrite() on a > VM_SHADOW_STACK VMA create the combination. > > Remove the checks, their callers and pud_shstk(), which has no other > user. > > In a KVM guest on Zen 4 with Safe RET, zapping 4K pages takes one branch > miss per page fewer. MADV_DONTNEED of 1 GiB gets 6% faster on anonymous > memory and 8% on shmem, munmap() 5%. THP is unchanged. Without Safe RET > the difference is within noise. Nice. > > Suggested-by: Dave Hansen > Signed-off-by: Kiryl Shutsemau (Meta) > --- > v2: > - Remove the checks instead of building them only with CONFIG_DEBUG_VM > (Dave Hansen). > - Drop the Fixes: tag (Rick Edgecombe). > - Note that without Safe RET the difference is within noise (Rick > Edgecombe). > - Drop Jose's Reviewed-by: the patch is new. > > v1: https://lore.kernel.org/all/20261102144001.342837-1-kas@kernel.org/ > Acked-by: Zi Yan --=20 Best Regards, Yan, Zi