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([2001:b07:6468:f312:1c09:f536:3de6:228c]) by smtp.googlemail.com with ESMTPSA id bm23-20020a170906c05700b006d597fd51c6sm2254888ejb.145.2022.03.25.04.27.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Mar 2022 04:27:03 -0700 (PDT) Message-ID: Date: Fri, 25 Mar 2022 12:26:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH] KVM: x86/mmu: Don't rebuild page when the page is synced and no tlb flushing is required Content-Language: en-US To: Sean Christopherson , Hou Wenlong Cc: kvm@vger.kernel.org, Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Lai Jiangshan , linux-kernel@vger.kernel.org References: <0dabeeb789f57b0d793f85d073893063e692032d.1647336064.git.houwenlong.hwl@antgroup.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/24/22 21:17, Sean Christopherson wrote: >> +static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, >> struct list_head *invalid_list) >> { >> int ret = vcpu->arch.mmu->sync_page(vcpu, sp); >> >> - if (ret < 0) { >> + if (ret < 0) >> kvm_mmu_prepare_zap_page(vcpu->kvm, sp, invalid_list); >> - return false; >> - } >> - >> - return !!ret; >> + return ret; > Hrm, this creates an oddity in mmu_sync_children(), which does a logical-OR of > the result into a boolean. It doesn't actually change the functionality since > kvm_mmu_remote_flush_or_zap() will prioritize invalid_list, but it's weird. > > What about checking invalid_list directly and keeping the boolean return? Compile > tested only. It's even better to check flush |= kvm_sync_page(vcpu, sp, &invalid_list) > 0; in mmu_sync_children. If the returned value is <0, then the page is added to invalid_list and there is no need to set flush = true, just like there is no need to call kvm_flush_remote_tlbs() in kvm_mmu_get_page(). Paolo