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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id n24sm10390224edv.51.2021.05.25.00.11.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 May 2021 00:11:12 -0700 (PDT) Subject: Re: [PATCH v2 5/5] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use To: Vitaly Kuznetsov , kvm@vger.kernel.org Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Maxim Levitsky , Kechen Lu , linux-kernel@vger.kernel.org References: <20210518144339.1987982-1-vkuznets@redhat.com> <20210518144339.1987982-6-vkuznets@redhat.com> <82e2a6a0-337a-4b92-2271-493344a38960@redhat.com> <87fsyb8h7s.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: <2b8d0e27-a893-b090-7ecd-df17eefdf6f1@redhat.com> Date: Tue, 25 May 2021 09:11:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <87fsyb8h7s.fsf@vitty.brq.redhat.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: kvm@vger.kernel.org On 25/05/21 08:23, Vitaly Kuznetsov wrote: >> Should it also disable APICv unconditionally if >> HV_DEPRECATING_AEOI_RECOMMENDED is not in the guest CPUID? That should >> avoid ping-pong between enabled and disabled APICv even in pathological >> cases that we cannot think about. > When you run Hyper-V on KVM it doesn't use SynIC (let alone AutoEOI) but > we still inhibit APICv unconditionally. The patch as-is improves this > without any userspace changes required and I see it as a benefit. Going > forward, we will definitely add something like 'hv-synic-noaeoi' to QEMU > to make non-nesting setups benefit too but it'll take a while for this > option to propagate to real world configurations (sigh). Ok, if enable<->disable APICv becomes an issue we can also consider disabling APICv forever if AutoEOI is ever used. Paolo