From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:56168 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728310AbeHMM2E (ORCPT ); Mon, 13 Aug 2018 08:28:04 -0400 Subject: Re: [PATCH v2 2/2] KVM: arm/arm64: Skip updating PTE entry if no change To: Punit Agrawal , kvmarm@lists.cs.columbia.edu Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, marc.zyngier@arm.com, christoffer.dall@arm.com, stable@vger.kernel.org References: <20180813094049.3726-1-punit.agrawal@arm.com> <20180813094049.3726-3-punit.agrawal@arm.com> From: Suzuki K Poulose Message-ID: <3ef331d7-d31a-a61b-7ad0-eb7c8bee10bd@arm.com> Date: Mon, 13 Aug 2018 10:47:15 +0100 MIME-Version: 1.0 In-Reply-To: <20180813094049.3726-3-punit.agrawal@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: On 08/13/2018 10:40 AM, Punit Agrawal wrote: > 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") > Change-Id: I28e17daf394a4821b13c2cf8726bf72bf30434f9 > Signed-off-by: Punit Agrawal > Cc: Marc Zyngier > Cc: Christoffer Dall > Cc: Suzuki Poulose > Cc: stable@vger.kernel.org > --- > virt/kvm/arm/mmu.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c > index 2ab977edc63c..d0a9dccc3793 100644 > --- a/virt/kvm/arm/mmu.c > +++ b/virt/kvm/arm/mmu.c > @@ -1120,6 +1120,10 @@ 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)) > + goto out; > + > kvm_set_pte(pte, __pte(0)); > kvm_tlb_flush_vmid_ipa(kvm, addr); > } else { > @@ -1127,6 +1131,7 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache, > } > > kvm_set_pte(pte, *new_pte); > +out: Similar comments as the previous patch, either way: Reviewed-by: Suzuki K Poulose