From c9fe66560bf2dc7d109754414e309888cb8c9ba9 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Mon, 9 May 2022 18:20:50 -0700 Subject: mm/mprotect: do not flush when not required architecturally Currently, using mprotect() to unprotect a memory region or uffd to unprotect a memory region causes a TLB flush. However, in such cases the PTE is often not modified (i.e., remain RO) and therefore not TLB flush is needed. Add an arch-specific pte_needs_flush() which tells whether a TLB flush is needed based on the old PTE and the new one. Implement an x86 pte_needs_flush(). Always flush the TLB when it is architecturally needed even when skipping a TLB flush might only result in a spurious page-faults by skipping the flush. Even with such conservative manner, we can in the future further refine the checks to test whether a PTE is present by only considering the architectural _PAGE_PRESENT flag instead of {pte|pmd}_preesnt(). For not be careful and use the latter. Link: https://lkml.kernel.org/r/20220401180821.1986781-3-namit@vmware.com Signed-off-by: Nadav Amit Cc: Andrea Arcangeli Cc: Andy Lutomirski Cc: Dave Hansen Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Cc: Yu Zhao Cc: Nick Piggin Cc: Andrew Cooper Cc: Peter Xu Signed-off-by: Andrew Morton --- include/asm-generic/tlb.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include') diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index eee6f7763a39..ff3e82553a76 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -658,6 +658,20 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb, } while (0) #endif +#ifndef pte_needs_flush +static inline bool pte_needs_flush(pte_t oldpte, pte_t newpte) +{ + return true; +} +#endif + +#ifndef huge_pmd_needs_flush +static inline bool huge_pmd_needs_flush(pmd_t oldpmd, pmd_t newpmd) +{ + return true; +} +#endif + #endif /* CONFIG_MMU */ #endif /* _ASM_GENERIC__TLB_H */ -- cgit