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([2001:b07:6468:f312:fd64:dd90:5ad5:d2e1]) by smtp.gmail.com with ESMTPSA id w7sm12908477wmc.32.2020.06.22.07.37.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Jun 2020 07:37:07 -0700 (PDT) Subject: Re: [PATCH v3] KVM: LAPIC: Recalculate apic map in batch To: Igor Mammedov Cc: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1582684862-10880-1-git-send-email-wanpengli@tencent.com> <20200619143626.1b326566@redhat.com> <3e025538-297b-74e5-f1b1-2193b614978b@redhat.com> <20200622002637.33358827@redhat.com> From: Paolo Bonzini Message-ID: Date: Mon, 22 Jun 2020 16:37:06 +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: <20200622002637.33358827@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 22/06/20 00:26, Igor Mammedov wrote: > > following sequence looks like a race that can cause lost map update events: > > cpu1 cpu2 > > apic_map_dirty = true > ------------------------------------------------------------ > kvm_recalculate_apic_map: > pass check > mutex_lock(&kvm->arch.apic_map_lock); > if (!kvm->arch.apic_map_dirty) > and in process of updating map > ------------------------------------------------------------- > other calls to > apic_map_dirty = true might be too late for affected cpu > ------------------------------------------------------------- > apic_map_dirty = false > ------------------------------------------------------------- > kvm_recalculate_apic_map: > bail out on > if (!kvm->arch.apic_map_dirty) I will post a fix for that. Thanks for the analysis! Paolo