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From: Maxim Levitsky <mlevitsk@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org
Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>,
	Wanpeng Li <wanpengli@tencent.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jim Mattson <jmattson@google.com>,
	Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH 5/6] KVM: x86: never clear irr_pending in kvm_apic_update_apicv
Date: Fri, 10 Dec 2021 15:10:34 +0200	[thread overview]
Message-ID: <8cbc67c742db2c4a66baf669a722a544d892ffb7.camel@redhat.com> (raw)
In-Reply-To: <3c30e682-a569-9e91-987d-9e2fc66bb625@redhat.com>

On Fri, 2021-12-10 at 14:03 +0100, Paolo Bonzini wrote:
> On 12/10/21 13:47, Maxim Levitsky wrote:
> > If we scan vIRR here and see no bits, and*then*  disable AVIC,
> > there is a window where the they could legit be turned on without any cpu errata,
> > and we will not have irr_pending == true, and thus the following
> > KVM_REQ_EVENT will make no difference.
> 
> Right.
> 
> > Not touching irr_pending and letting just the KVM_REQ_EVENT do the work
> > will work too,
> 
> Yeah, I think that's preferrable.  irr_pending == true is a conservative 
> setting that works; irr_pending will be evaluated again on the first 
> call to apic_clear_irr and that's enough.
> 
> With that justification, you don't need to reorder the call to 
> kvm_apic_update_apicv to be after kvm_x86_refresh_apicv_exec_ctrl.

Yes exactly! but no need to scan IRR here since irr_pending is already
true at that point anyway - it is always true while avic is enabled.


Best regards,
	Maxim Levitsky
> 
> Paolo
> 
>   and if the avic errata is present, reduce slightly
> > the chances of it happening.



  reply	other threads:[~2021-12-10 13:10 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-09 11:54 [PATCH 0/6] RFC: KVM: SVM: Allow L1's AVIC to co-exist with nesting Maxim Levitsky
2021-12-09 11:54 ` [PATCH 1/6] KVM: SVM: allow to force AVIC to be enabled Maxim Levitsky
2021-12-09 11:54 ` [PATCH 2/6] KVM: x86: add a tracepoint for APICv/AVIC interrupt delivery Maxim Levitsky
2021-12-09 11:54 ` [PATCH 3/6] KVM: SVM: fix AVIC race of host->guest IPI delivery vs AVIC inhibition Maxim Levitsky
2021-12-09 14:11   ` Paolo Bonzini
2021-12-09 14:26     ` Maxim Levitsky
2021-12-09 15:27       ` Sean Christopherson
2021-12-09 15:33         ` Maxim Levitsky
2021-12-09 15:35           ` Maxim Levitsky
2021-12-09 11:54 ` [PATCH 4/6] KVM: SVM: fix races in the AVIC incomplete IPI delivery to vCPUs Maxim Levitsky
2021-12-09 15:38   ` Sean Christopherson
2021-12-10 11:37     ` Paolo Bonzini
2021-12-09 11:54 ` [PATCH 5/6] KVM: x86: never clear irr_pending in kvm_apic_update_apicv Maxim Levitsky
2021-12-09 14:12   ` Paolo Bonzini
2021-12-09 15:03     ` Maxim Levitsky
2021-12-10 12:07   ` Paolo Bonzini
2021-12-10 12:20     ` Maxim Levitsky
2021-12-10 12:47       ` Maxim Levitsky
2021-12-10 13:03         ` Paolo Bonzini
2021-12-10 13:10           ` Maxim Levitsky [this message]
2021-12-09 11:54 ` [PATCH 6/6] KVM: SVM: allow AVIC to co-exist with a nested guest running Maxim Levitsky

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