FAILED: patch "[PATCH] KVM: arm/arm64: Skip updating PTE entry if no change" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Punit Agrawal <[email protected]>
Date: Mon, 13 Aug 2018 11:43:51 +0100
Subject: [PATCH] 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.

index 13dfe36501aa..91aaf73b00df 100644
@@ -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 {

This patch fails to apply for similar reason as to the PMD one I just sent out. Please find the backport patch below.

Thanks,
Punit

-- >8 --
From: Punit Agrawal <[email protected]>
Date: Fri, 10 Aug 2018 20:05:07 +0100
Subject: [PATCH 2/2] KVM: arm/arm64: Skip updating PTE entry if no change

commit 976d34e2dab10ece5ea8fe7090b7692913f89084 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.

---
 arch/arm/kvm/mmu.c | 4 ++++
 1 file changed, 4 insertions(+)

index e3acb3a6ca37..b3d268a79f05 100644
@@ -978,6 +978,10 @@ 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 {

2.18.0