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: [email protected] Fixes: d5d8184 ("KVM: ARM: Memory virtualization setup") Reviewed-by: Suzuki Poulose <[email protected]> Acked-by: Christoffer Dall <[email protected]> Signed-off-by: Punit Agrawal <[email protected]> Signed-off-by: Marc Zyngier <[email protected]>
josf · Aug 13, 2018 · 976d34e · 976d34e
1 parent 86658b8
commit 976d34e
Showing 1 changed file with 4 additions and 0 deletions.
diff --git 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 {