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KVM: arm/arm64: Skip updating PTE entry if no change

commit 976d34e upstream.

When there is contention on faulting in a particular page table entry
at stage 2, the break-before-make requirement of the architecture can
lead to additional refaulting due to TLB invalidation.

Avoid this by skipping a page table update if the new value of the PTE
matches the previous value.

Fixes: d5d8184 ("KVM: ARM: Memory virtualization setup")
Reviewed-by: Suzuki Poulose <>
Acked-by: Christoffer Dall <>
Signed-off-by: Punit Agrawal <>
Signed-off-by: Marc Zyngier <>
Signed-off-by: Greg Kroah-Hartman <>
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punitagrawal authored and gregkh committed Aug 13, 2018
1 parent 792a039 commit 4a06fdf2c490666e7e8d2a3c17adfff3f0354441
Showing with 4 additions and 0 deletions.
  1. +4 −0 virt/kvm/arm/mmu.c
@@ -985,6 +985,10 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
/* Create 2nd stage page table mapping - Level 3 */
old_pte = *pte;
if (pte_present(old_pte)) {
/* Skip page table update if there is no change */
if (pte_val(old_pte) == pte_val(*new_pte))
return 0;
kvm_set_pte(pte, __pte(0));
kvm_tlb_flush_vmid_ipa(kvm, addr);
} else {

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