Subject: Re: [PATCH 13/14] KVM: x86: Directly block (instead of "halting") UNINITIALIZED vCPUs

From: David Matlack <[email-masked]>
Date: Tue, 28 Sep 2021 22:12:50 +0000

On Fri, Sep 24, 2021 at 05:55:27PM -0700, Sean Christopherson wrote:
> Go directly to kvm_vcpu_block() when handling the case where userspace
> attempts to run an UNINITIALIZED vCPU.  The vCPU isn't halted and its time
> spent in limbo arguably should not be factored into halt-polling as the
> behavior of the VM at this point is not at all indicative of the behavior
> of the VM once it is up and running, i.e. executing HLT in idle tasks.
> 
> Note, because this case is encountered only on the first run of an AP vCPU,
> vcpu->halt_poll_ns is guaranteed to be '0', and so KVM will not attempt
> halt-polling, i.e. this really only affects the post-block bookkeeping.
> 
> Signed-off-by: Sean Christopherson <[email-masked]>

Reviewed-by: David Matlack <[email-masked]>

> ---
>  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 0d71c73a61bb..b444f9315766 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10127,7 +10127,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>  			r = -EINTR;
>  			goto out;
>  		}
> -		kvm_vcpu_halt(vcpu);
> +		kvm_vcpu_block(vcpu);
>  		if (kvm_apic_accept_events(vcpu) < 0) {
>  			r = 0;
>  			goto out;
> -- 
> 2.33.0.685.g46640cef36-goog
> 

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