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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id e25sm1449631wra.71.2020.11.06.02.18.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Nov 2020 02:18:02 -0800 (PST) Subject: Re: [PATCH] x86/kvm/hyper-v: Don't deactivate APICv unconditionally when Hyper-V SynIC enabled To: Vitaly Kuznetsov , junjiehua0xff@gmail.com Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel , Andrey Smetanin , Junjie Hua , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <1604567537-909-1-git-send-email-junjiehua@tencent.com> <87sg9n3ilt.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: <348f8763-3842-0dda-2c01-6c5d510fe630@redhat.com> Date: Fri, 6 Nov 2020 11:18:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <87sg9n3ilt.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: linux-kernel@vger.kernel.org On 05/11/20 16:53, Vitaly Kuznetsov wrote: >> The current implementation of Hyper-V SynIC[1] request to deactivate >> APICv when SynIC is enabled, since the AutoEOI feature of SynIC is not >> compatible with APICv[2]. >> >> Actually, windows doesn't use AutoEOI if deprecating AutoEOI bit is set >> (CPUID.40000004H:EAX[bit 9], HyperV-TLFS v6.0b section 2.4.5), we don't >> need to disable APICv in this case. >> > Thank you for the patch, the fact that we disable APICv every time we > enable SynIC is nothing to be proud of. I'm, however, not sure we can > treat 'Recommend deprecating AutoEOI' as 'AutoEOI must not be > used.'. Could you please clarify which Windows versions you've tested > with with? > Indeed---older versions of Windows that predate the deprecation will continue using AutoEOI. Paolo