linux-kernel - Re: [PATCH v2] x86/kvm/vmx: Don't halt vcpu when L1 is injecting events to L2

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Date:   Fri, 9 Feb 2018 16:31:22 -0800 (PST)
From:   Liran Alon <liran.alon@...cle.com>
To:     <chao.gao@...el.com>
Cc:     <mingo@...hat.com>, <x86@...nel.org>, <tglx@...utronix.de>,
        <rkrcmar@...hat.com>, <pbonzini@...hat.com>,
        <linux-kernel@...r.kernel.org>, <hpa@...or.com>,
        <kvm@...r.kernel.org>
Subject: Re: [PATCH v2] x86/kvm/vmx: Don't halt vcpu when L1 is injecting
 events to L2


----- chao.gao@...el.com wrote:

> Although L2 is in halt state, it will be in the active state after
> VM entry if the VM entry is vectoring according to SDM 26.6.2
> Activity
> State. Halting the vcpu here means the event won't be injected to L2
> and this decision isn't reported to L1. Thus L0 drops an event that
> should be injected to L2.
> 
> Cc: Liran Alon <liran.alon@...cle.com>
> Signed-off-by: Chao Gao <chao.gao@...el.com>
> ---
> Changes in v2:
>  - Remove VID stuff. Only handle event injection in this patch.
> ---
>  arch/x86/kvm/vmx.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index bb5b488..42f39d9 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -10985,7 +10985,12 @@ static int nested_vmx_run(struct kvm_vcpu
> *vcpu, bool launch)
>  	if (ret)
>  		return ret;
>  
> -	if (vmcs12->guest_activity_state == GUEST_ACTIVITY_HLT)
> +	/*
> +	 * If we're entering a halted L2 vcpu and the L2 vcpu won't be
> woken
> +	 * by event injection, halt vcpu for optimization.

I would remove the "for optimization." from the comment.

> +	 */
> +	if ((vmcs12->guest_activity_state == GUEST_ACTIVITY_HLT) &&
> +	    !(vmcs12->vm_entry_intr_info_field &
> VECTORING_INFO_VALID_MASK))

VECTORING_INFO_VALID_MASK is used in KVM code against vmcs12->idt_vectoring_info_field.
I think you should use INTR_INFO_VALID_MASK to be consistent with rest of code.

>  		return kvm_vcpu_halt(vcpu);
>  
>  	vmx->nested.nested_run_pending = 1;
> -- 
> 1.9.1

In addition, commit title should be written in format of:
"KVM: VMX: Don't halt vcpu when L1 is injecting events to L2"
(Makes it easier to grep in git log).

Other than that, seems good to me. :)

Reviewed-by: Liran Alon <liran.alon@...cle.com>

Thanks,
-Liran