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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id g1sm32214606wrq.30.2021.01.18.09.34.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Jan 2021 09:34:11 -0800 (PST) Subject: Re: [PATCH] KVM: x86: Zap the oldest MMU pages, not the newest To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Zdenek Kaspar References: <20210113205030.3481307-1-seanjc@google.com> From: Paolo Bonzini Message-ID: <0e8b9adb-1010-1b76-620b-4235eee405cf@redhat.com> Date: Mon, 18 Jan 2021 18:34:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210113205030.3481307-1-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/01/21 21:50, Sean Christopherson wrote: > Walk the list of MMU pages in reverse in kvm_mmu_zap_oldest_mmu_pages(). > The list is FIFO, meaning new pages are inserted at the head and thus > the oldest pages are at the tail. Using a "forward" iterator causes KVM > to zap MMU pages that were just added, which obliterates guest > performance once the max number of shadow MMU pages is reached. > > Fixes: 6b82ef2c9cf1 ("KVM: x86/mmu: Batch zap MMU pages when recycling oldest pages") > Reported-by: Zdenek Kaspar > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 6d16481aa29d..ed861245ecf0 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -2417,7 +2417,7 @@ static unsigned long kvm_mmu_zap_oldest_mmu_pages(struct kvm *kvm, > return 0; > > restart: > - list_for_each_entry_safe(sp, tmp, &kvm->arch.active_mmu_pages, link) { > + list_for_each_entry_safe_reverse(sp, tmp, &kvm->arch.active_mmu_pages, link) { > /* > * Don't zap active root pages, the page itself can't be freed > * and zapping it will just force vCPUs to realloc and reload. > Queued for 5.11, thanks. Paolo