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 {