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

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.

Cc: stable@vger.kernel.org
Fixes: d5d8184d35c9 ("KVM: ARM: Memory virtualization setup")
Reviewed-by: Suzuki Poulose <suzuki.poulose@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 13dfe36501aa9781d803cab2b7586adc3f6c2d4b..91aaf73b00df8a385a28c2a221505b6ba82062b1 100644 (file)
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1147,6 +1147,10 @@ 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 {