Re: [PATCH 2/2] KVM: x86: Identify vCPU0 by its vcpu_idx instead of walking vCPUs array

From: Maxim Levitsky <mlevitsk@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@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: Sun, 12 Sep 2021 13:52:43 +0300	[thread overview]
Message-ID: <71a6464fa0bca675e079f6171296ff5f63cab05c.camel@redhat.com> (raw)
In-Reply-To: <20210910183220.2397812-3-seanjc@google.com>

On Fri, 2021-09-10 at 11:32 -0700, Sean Christopherson wrote:
> 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;
>  }
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky