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

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

[gregkh]

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 <stable@vger.kernel.org>.

thanks,

greg k-h

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

>From 976d34e2dab10ece5ea8fe7090b7692913f89084 Mon Sep 17 00:00:00 2001
From: Punit Agrawal <punit.agrawal@arm.com>
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.

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 13dfe36501aa..91aaf73b00df 100644
--- 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 {

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

[Punit Agrawal]

<gregkh@linuxfoundation.org> writes:

> 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 <stable@vger.kernel.org>.

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 <punit.agrawal@arm.com>
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.

Fixes: d5d8184d35c9 ("KVM: ARM: Memory virtualization setup")
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Reviewed-by: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
---
 arch/arm/kvm/mmu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index e3acb3a6ca37..b3d268a79f05 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -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