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([2001:b07:6468:f312:3c1c:ffba:c624:29b8]) by smtp.gmail.com with ESMTPSA id a124sm6527861wmh.4.2020.05.28.04.44.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 May 2020 04:44:14 -0700 (PDT) Subject: Re: [PATCH v2 06/10] KVM: x86: acknowledgment mechanism for async pf page ready notifications To: Vitaly Kuznetsov , kvm@vger.kernel.org, x86@kernel.org Cc: Andy Lutomirski , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" , Wanpeng Li , Sean Christopherson , Jim Mattson , Vivek Goyal , Gavin Shan , Peter Zijlstra , linux-kernel@vger.kernel.org References: <20200525144125.143875-1-vkuznets@redhat.com> <20200525144125.143875-7-vkuznets@redhat.com> <87wo4w2sra.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: <690f1a02-6077-e971-f2e9-aedd89f0901a@redhat.com> Date: Thu, 28 May 2020 13:44:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <87wo4w2sra.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/05/20 13:39, Vitaly Kuznetsov wrote: >> How is the pageready_pending flag migrated? Should we revert the >> direction of the MSR (i.e. read the flag, and write 0 to clear it)? > The flag is not migrated so it will be 'false'. This can just cause an > extra kick in kvm_arch_async_page_present_queued() but this shouldn't be > a big deal. Also, after migration we will just send 'wakeup all' event, > async pf queue will be empty. Ah, that's kvm_pv_enable_async_pf, where the destination writes to MSR_KVM_ASYNC_PF. Cool. > MSR_KVM_ASYNC_PF_ACK by itself is not > migrated, we don't even store it, not sure how invering it would change > things. Yes, it would only be useful to invert it if it needs to be stored and migrated. Thanks, Paolo