linux-kernel - Re: [PATCH v2] KVM: x86: check PIR even for vCPUs with disabled APICv

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Message-ID: <5d170d5242f1cd9b291f3171120b86d2f2941229.camel@redhat.com>
Date:   Thu, 18 Nov 2021 13:17:50 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2] KVM: x86: check PIR even for vCPUs with disabled
 APICv

On Thu, 2021-11-18 at 12:11 +0100, Paolo Bonzini wrote:
> On 11/18/21 10:56, Maxim Levitsky wrote:
> > vmx_sync_pir_to_irr has 'if (KVM_BUG_ON(!vcpu->arch.apicv_active,
> > vcpu->kvm))' That has to be removed I think for this to work.
> 
> Good point.
> 
> > Plus the above calls now can happen when APICv is fully disabled (and
> > not just inhibited), which is also something that I think that
> > vmx_sync_pir_to_irr should be fixed to be aware of.
> 
> No, that works because sync_pir_to_irr is set to NULL as you point out 
> below.  static_call sites are updated right after ops->hardware_setup(), 
> in kvm_arch_hardware_setup.

I understand now. Thanks!

Best regards,
	Maxim Levitsky

> 
> Paolo
> 
> > Also note that VMX has code that sets vmx_x86_ops.sync_pir_to_irr to
> > NULL in its 'hardware_setup' if APICv is disabled. I wonder if that
> > done befor or after the static_call_cond sites are updated.
> > 
> > I think that this code should be removed as well, and
> > vmx_sync_pir_to_irr should just do nothing when APICv is fully
> > disabled.