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From: Sean Christopherson via iommu <iommu@lists.linux-foundation.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Maxim Levitsky <mlevitsk@redhat.com>,
	iommu@lists.linux-foundation.org,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jim Mattson <jmattson@google.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).
> 	 */
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WARNING: multiple messages have this Message-ID (diff)
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).
> 	 */

  parent reply	other threads:[~2021-12-08 15:43 UTC|newest]

Thread overview: 96+ 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 via iommu
2021-12-08  1:52 ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 01/26] KVM: fix avic_set_running for preemptable kernels Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 03/26] KVM: VMX: Clean up PI pre/post-block WARNs Sean Christopherson via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 04/26] KVM: VMX: Handle PI wakeup shenanigans during vcpu_put/load Sean Christopherson via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 05/26] KVM: Drop unused kvm_vcpu.pre_pcpu field Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 07/26] KVM: VMX: Move preemption timer <=> hrtimer dance to common x86 Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 10/26] KVM: SVM: Signal AVIC doorbell iff vCPU is in guest mode Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 12/26] KVM: SVM: Remove unnecessary APICv/AVIC update in vCPU unblocking path Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 14/26] KVM: SVM: Skip AVIC and IRTE updates when loading blocking vCPU Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 19/26] KVM: VMX: Fold fallback path into triggering posted IRQ helper Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 21/26] KVM: SVM: Drop AVIC's intermediate avic_set_running() helper Sean Christopherson via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08 14:43   ` Paolo Bonzini
2021-12-08 14:43     ` Paolo Bonzini
2021-12-08 15:03     ` Maxim Levitsky
2021-12-08 15:03       ` Maxim Levitsky
2021-12-08 15:43     ` Sean Christopherson via iommu [this message]
2021-12-08 15:43       ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 22/26] KVM: SVM: Move svm_hardware_setup() and its helpers below svm_x86_ops Sean Christopherson via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 23/26] KVM: SVM: Nullify vcpu_(un)blocking() hooks if AVIC is disabled Sean Christopherson via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` 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 via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  1:52 ` [PATCH v3 26/26] KVM: x86: Unexport __kvm_request_apicv_update() Sean Christopherson via iommu
2021-12-08  1:52   ` Sean Christopherson
2021-12-08  9:04 ` [PATCH v3 00/26] KVM: x86: Halt and APICv overhaul Paolo Bonzini
2021-12-08  9:04   ` Paolo Bonzini
2021-12-08 14:51 ` Paolo Bonzini
2021-12-08 14:51   ` Paolo Bonzini
2021-12-08 23:00 ` Maxim Levitsky
2021-12-08 23:00   ` Maxim Levitsky
2021-12-08 23:16   ` Maxim Levitsky
2021-12-08 23:16     ` Maxim Levitsky
2021-12-08 23:34     ` Maxim Levitsky
2021-12-08 23:34       ` Maxim Levitsky
2021-12-09  0:04       ` Sean Christopherson via iommu
2021-12-09  0:04         ` Sean Christopherson
2021-12-09  6:36         ` Maxim Levitsky
2021-12-09  6:36           ` Maxim Levitsky
2021-12-09  0:02     ` Sean Christopherson via iommu
2021-12-09  0:02       ` Sean Christopherson
2021-12-09 14:29       ` Paolo Bonzini
2021-12-09 14:29         ` Paolo Bonzini
2021-12-09 14:48         ` Maxim Levitsky
2021-12-09 14:48           ` Maxim Levitsky
2021-12-09 15:45           ` Sean Christopherson via iommu
2021-12-09 15:45             ` Sean Christopherson
2021-12-09 16:03             ` Maxim Levitsky
2021-12-09 16:03               ` Maxim Levitsky
2021-12-09  1:37     ` Sean Christopherson via iommu
2021-12-09  1:37       ` Sean Christopherson
2021-12-09  6:31       ` Maxim Levitsky
2021-12-09  6:31         ` Maxim Levitsky
2021-12-08 23:43   ` Sean Christopherson via iommu
2021-12-08 23:43     ` Sean Christopherson
2021-12-09  6:34     ` Maxim Levitsky
2021-12-09  6:34       ` Maxim Levitsky

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