From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
kvm@vger.kernel.org, iommu@lists.linux-foundation.org,
linux-kernel@vger.kernel.org,
Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH v3 21/26] KVM: SVM: Drop AVIC's intermediate avic_set_running() helper
Date: Wed, 8 Dec 2021 15:43:16 +0000 [thread overview]
Message-ID: <YbDSlNsY8b2O8PtM@google.com> (raw)
In-Reply-To: <e1c4ec6a-7c1e-b96c-63e6-d07b35820def@redhat.com>
On Wed, Dec 08, 2021, Paolo Bonzini wrote:
> On 12/8/21 02:52, Sean Christopherson wrote:
> > + /*
> > + * Unload the AVIC when the vCPU is about to block,_before_ the vCPU
> > + * actually blocks. The vCPU needs to be marked IsRunning=0 before the
> > + * final pass over the vIRR via kvm_vcpu_check_block(). Any IRQs that
> > + * arrive before IsRunning=0 will not signal the doorbell, i.e. it's
> > + * KVM's responsibility to ensure there are no pending IRQs in the vIRR
> > + * after IsRunning is cleared, prior to scheduling out the vCPU.
>
> I prefer to phrase this around paired memory barriers and the usual
> store/smp_mb/load lockless idiom:
I've no objection to that, my goal is/was purely to emphasize the need to manually
process the vIRR after clearing IsRunning.
> /*
> * Unload the AVIC when the vCPU is about to block, _before_
> * the vCPU actually blocks.
> *
> * Any IRQs that arrive before IsRunning=0 will not cause an
> * incomplete IPI vmexit on the source,
It's not just IPIs, the GA log will also suffer the same fate. That's why I
didn't mention incomplete VM-Exits. I'm certainly not opposed to that clarification,
but I don't want readers to walk away thinking this is only a problem for IPIs.
> therefore vIRR will also
"s/vIRR will/the vIRR must" to make it abundantly clear that checking the vIRR
is effectively a hard requirement.
> * be checked by kvm_vcpu_check_block() before blocking. The
> * memory barrier implicit in set_current_state orders writing
set_current_state()
> * IsRunning=0 before reading the vIRR. The processor needs a
> * matching memory barrier on interrupt delivery between writing
> * IRR and reading IsRunning; the lack of this barrier might be
Missing the opening paranthesis.
> * the cause of errata #1235).
> */
next prev parent reply other threads:[~2021-12-08 15:43 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-08 1:52 [PATCH v3 00/26] KVM: x86: Halt and APICv overhaul Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 01/26] KVM: fix avic_set_running for preemptable kernels Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 02/26] KVM: nVMX: Ensure vCPU honors event request if posting nested IRQ fails Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 03/26] KVM: VMX: Clean up PI pre/post-block WARNs Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 04/26] KVM: VMX: Handle PI wakeup shenanigans during vcpu_put/load Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 05/26] KVM: Drop unused kvm_vcpu.pre_pcpu field Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 06/26] KVM: Move x86 VMX's posted interrupt list_head to vcpu_vmx Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 07/26] KVM: VMX: Move preemption timer <=> hrtimer dance to common x86 Sean Christopherson
2023-03-29 12:34 ` Tudor Ambarus
2023-03-29 13:47 ` Paolo Bonzini
2023-03-29 15:22 ` Tudor Ambarus
2023-03-30 7:12 ` Tudor Ambarus
2021-12-08 1:52 ` [PATCH v3 08/26] KVM: x86: Unexport LAPIC's switch_to_{hv,sw}_timer() helpers Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 09/26] KVM: x86: Remove defunct pre_block/post_block kvm_x86_ops hooks Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 10/26] KVM: SVM: Signal AVIC doorbell iff vCPU is in guest mode Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 11/26] KVM: SVM: Don't bother checking for "running" AVIC when kicking for IPIs Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 12/26] KVM: SVM: Remove unnecessary APICv/AVIC update in vCPU unblocking path Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 13/26] KVM: SVM: Use kvm_vcpu_is_blocking() in AVIC load to handle preemption Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 14/26] KVM: SVM: Skip AVIC and IRTE updates when loading blocking vCPU Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 15/26] iommu/amd: KVM: SVM: Use pCPU to infer IsRun state for IRTE Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 16/26] KVM: VMX: Don't do full kick when triggering posted interrupt "fails" Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 17/26] KVM: VMX: Wake vCPU when delivering posted IRQ even if vCPU == this vCPU Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 18/26] KVM: VMX: Pass desired vector instead of bool for triggering posted IRQ Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 19/26] KVM: VMX: Fold fallback path into triggering posted IRQ helper Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 20/26] KVM: VMX: Don't do full kick when handling posted interrupt wakeup Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 21/26] KVM: SVM: Drop AVIC's intermediate avic_set_running() helper Sean Christopherson
2021-12-08 14:43 ` Paolo Bonzini
2021-12-08 15:03 ` Maxim Levitsky
2021-12-08 15:43 ` Sean Christopherson [this message]
2021-12-08 1:52 ` [PATCH v3 22/26] KVM: SVM: Move svm_hardware_setup() and its helpers below svm_x86_ops Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 23/26] KVM: SVM: Nullify vcpu_(un)blocking() hooks if AVIC is disabled Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 24/26] KVM: x86: Skip APICv update if APICv is disable at the module level Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 25/26] KVM: x86: Drop NULL check on kvm_x86_ops.check_apicv_inhibit_reasons Sean Christopherson
2021-12-08 1:52 ` [PATCH v3 26/26] KVM: x86: Unexport __kvm_request_apicv_update() Sean Christopherson
2021-12-08 9:04 ` [PATCH v3 00/26] KVM: x86: Halt and APICv overhaul Paolo Bonzini
2021-12-08 14:51 ` Paolo Bonzini
2021-12-08 23:00 ` Maxim Levitsky
2021-12-08 23:16 ` Maxim Levitsky
2021-12-08 23:34 ` Maxim Levitsky
2021-12-09 0:04 ` Sean Christopherson
2021-12-09 6:36 ` Maxim Levitsky
2021-12-09 0:02 ` Sean Christopherson
2021-12-09 14:29 ` Paolo Bonzini
2021-12-09 14:48 ` Maxim Levitsky
2021-12-09 15:45 ` Sean Christopherson
2021-12-09 16:03 ` Maxim Levitsky
2021-12-09 1:37 ` Sean Christopherson
2021-12-09 6:31 ` Maxim Levitsky
2021-12-08 23:43 ` Sean Christopherson
2021-12-09 6:34 ` Maxim Levitsky
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