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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id d17sm17979027pfj.215.2021.11.29.10.55.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Nov 2021 10:55:18 -0800 (PST) Date: Mon, 29 Nov 2021 18:55:14 +0000 From: Sean Christopherson To: Paolo Bonzini Cc: Maxim Levitsky , Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang Subject: Re: [PATCH v2 11/43] KVM: Don't block+unblock when halt-polling is successful Message-ID: References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-12-seanjc@google.com> <4e883728e3e5201a94eb46b56315afca5e95ad9c.camel@redhat.com> <496c2fc6-26b0-9b5d-32f4-2f9e9dd6a064@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <496c2fc6-26b0-9b5d-32f4-2f9e9dd6a064@redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Nov 29, 2021, Paolo Bonzini wrote: > On 11/29/21 18:25, Sean Christopherson wrote: > > If a posted interrupt arrives after KVM has done its final search through the vIRR, > > but before avic_update_iommu_vcpu_affinity() is called, the posted interrupt will > > be set in the vIRR without triggering a host IRQ to wake the vCPU via the GA log. > > > > I.e. KVM is missing an equivalent to VMX's posted interrupt check for an outstanding > > notification after switching to the wakeup vector. > > BTW Maxim reported that it can break even without assigned devices. > > > For now, the least awful approach is sadly to keep the vcpu_(un)blocking() hooks. > > I agree that the hooks cannot be dropped but the bug is reproducible with > this patch, where the hooks are still there. ... > Still it does seem to be a race that happens when IS_RUNNING=true but > vcpu->mode == OUTSIDE_GUEST_MODE. This patch makes the race easier to > trigger because it moves IS_RUNNING=false later. Oh! Any chance the bug only repros with preemption enabled? That would explain why I don't see problems, I'm pretty sure I've only run AVIC with a PREEMPT=n. svm_vcpu_{un}blocking() are called with preemption enabled, and avic_set_running() passes in vcpu->cpu. If the vCPU is preempted and scheduled in on a different CPU, avic_vcpu_load() will overwrite the vCPU's entry with the wrong CPU info.