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From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: Identify vCPU0 by its vcpu_idx instead of walking vCPUs array
Date: Mon, 20 Sep 2021 14:57:15 +0000	[thread overview]
Message-ID: <YUihS9CcTh9m53J6@google.com> (raw)
In-Reply-To: <87czpd2bsi.fsf@vitty.brq.redhat.com>

On Mon, Sep 13, 2021, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > Use vcpu_idx to identify vCPU0 when updating HyperV's TSC page, which is
> > shared by all vCPUs and "owned" by vCPU0 (because vCPU0 is the only vCPU
> > that's guaranteed to exist).  Using kvm_get_vcpu() to find vCPU works,
> > but it's a rather odd and suboptimal method to check the index of a given
> > vCPU.
> >
> > No functional change intended.
> >
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  arch/x86/kvm/x86.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 86539c1686fa..6ab851df08d1 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2969,7 +2969,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> >  				       offsetof(struct compat_vcpu_info, time));
> >  	if (vcpu->xen.vcpu_time_info_set)
> >  		kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0);
> > -	if (v == kvm_get_vcpu(v->kvm, 0))
> > +	if (!v->vcpu_idx)
> >  		kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
> >  	return 0;
> >  }
> 
> " ... instead of walking vCPUs array" in the Subject line is a bit
> confusing because kvm_get_vcpu() doesn't actually walk anything, it just
> returns 'kvm->vcpus[i]' after checking that we actually have that many
> vCPUs. The patch itself is OK, so

Argh, yes, I have a feeling I wrote the changelog after digging into the history
of kvm_get_vcpu().

Paolo, can you tweak the shortlog to:

  KVM: x86: Identify vCPU0 by its vcpu_idx instead of its vCPUs array entry

  reply	other threads:[~2021-09-20 14:57 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 18:32 [PATCH 0/2] KVM: x86: vcpu_idx related cleanups Sean Christopherson
2021-09-10 18:32 ` [PATCH 1/2] KVM: x86: Query vcpu->vcpu_idx directly and drop its accessor Sean Christopherson
2021-09-12 10:49   ` Maxim Levitsky
2021-09-13  7:02   ` Vitaly Kuznetsov
2021-09-10 18:32 ` [PATCH 2/2] KVM: x86: Identify vCPU0 by its vcpu_idx instead of walking vCPUs array Sean Christopherson
2021-09-10 21:46   ` Jim Mattson
2021-09-12 10:52   ` Maxim Levitsky
2021-09-13  7:07   ` Vitaly Kuznetsov
2021-09-20 14:57     ` Sean Christopherson [this message]
2021-09-22  7:41       ` Paolo Bonzini

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