diff options
| author | Nadav Amit <namit@vmware.com> | 2022-05-10 03:20:50 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2022-05-13 16:20:05 +0200 |
| commit | c9fe66560bf2dc7d109754414e309888cb8c9ba9 (patch) | |
| tree | b609e89d09822a588f5445e736edc83e5b34af35 /mm | |
| parent | mm/mprotect: use mmu_gather (diff) | |
| download | linux-c9fe66560bf2dc7d109754414e309888cb8c9ba9.tar.xz linux-c9fe66560bf2dc7d109754414e309888cb8c9ba9.zip | |
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')
| -rw-r--r-- | mm/huge_memory.c | 9 | ||||
| -rw-r--r-- | mm/mprotect.c | 3 |
2 files changed, 7 insertions, 5 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 8db17c042aed..2befa9cfb46e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1715,7 +1715,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, { struct mm_struct *mm = vma->vm_mm; spinlock_t *ptl; - pmd_t entry; + pmd_t oldpmd, entry; bool preserve_write; int ret; bool prot_numa = cp_flags & MM_CP_PROT_NUMA; @@ -1804,9 +1804,9 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, * pmdp_invalidate() is required to make sure we don't miss * dirty/young flags set by hardware. */ - entry = pmdp_invalidate(vma, addr, pmd); + oldpmd = pmdp_invalidate(vma, addr, pmd); - entry = pmd_modify(entry, newprot); + entry = pmd_modify(oldpmd, newprot); if (preserve_write) entry = pmd_mk_savedwrite(entry); if (uffd_wp) { @@ -1823,7 +1823,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, ret = HPAGE_PMD_NR; set_pmd_at(mm, addr, pmd, entry); - tlb_flush_pmd_range(tlb, addr, HPAGE_PMD_SIZE); + if (huge_pmd_needs_flush(oldpmd, entry)) + tlb_flush_pmd_range(tlb, addr, HPAGE_PMD_SIZE); BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry)); unlock: 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); |