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authorNadav Amit <namit@vmware.com>2022-05-10 04:20:50 +0300
committerAndrew Morton <akpm@linux-foundation.org>2022-05-13 17:20:05 +0300
commitc9fe66560bf2dc7d109754414e309888cb8c9ba9 (patch)
treeb609e89d09822a588f5445e736edc83e5b34af35 /mm/mprotect.c
parent4a18419f71cdf9155d2d2a6c79546f720978b990 (diff)
downloadlinux-c9fe66560bf2dc7d109754414e309888cb8c9ba9.tar.xz
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 <namit@vmware.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will@kernel.org> Cc: Yu Zhao <yuzhao@google.com> Cc: Nick Piggin <npiggin@gmail.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/mprotect.c')
-rw-r--r--mm/mprotect.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 420be0201118..20a46f21cca8 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -152,7 +152,8 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
ptent = pte_mkwrite(ptent);
}
ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
- tlb_flush_pte_range(tlb, addr, PAGE_SIZE);
+ if (pte_needs_flush(oldpte, ptent))
+ tlb_flush_pte_range(tlb, addr, PAGE_SIZE);
pages++;
} else if (is_swap_pte(oldpte)) {
swp_entry_t entry = pte_to_swp_entry(oldpte);