linux-kernel - Re: [PATCH v2 6/9] KVM: x86: make vendor code check for all nested events

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Message-ID: <Yvwsf61D8wbwkAh7@google.com>
Date:   Tue, 16 Aug 2022 23:47:11 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        mlevitsk@...hat.com, vkuznets@...hat.com
Subject: Re: [PATCH v2 6/9] KVM: x86: make vendor code check for all nested
 events

On Thu, Aug 11, 2022, Paolo Bonzini wrote:
> Interrupts, NMIs etc. sent while in guest mode are already handled
> properly by the *_interrupt_allowed callbacks, but other events can
> cause a vCPU to be runnable that are specific to guest mode.
> 
> In the case of VMX there are two, the preemption timer and the
> monitor trap.  The VMX preemption timer is already special cased via
> the hv_timer_pending callback, but the purpose of the callback can be
> easily extended to MTF or in fact any other event that can occur only
> in guest mode.
> 
> Rename the callback and add an MTF check; kvm_arch_vcpu_runnable()
> now will return true if an MTF is pending, without relying on
> kvm_vcpu_running()'s call to kvm_check_nested_events().  Until that call
> is removed, however, the patch introduces no functional change.
> 
> Reported-by: Maxim Levitsky <mlevitsk@...hat.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 +-
>  arch/x86/kvm/vmx/nested.c       | 9 ++++++++-
>  arch/x86/kvm/x86.c              | 8 ++++----
>  3 files changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 5ffa578cafe1..293ff678fff5 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1636,7 +1636,7 @@ struct kvm_x86_nested_ops {
>  	int (*check_events)(struct kvm_vcpu *vcpu);
>  	bool (*handle_page_fault_workaround)(struct kvm_vcpu *vcpu,
>  					     struct x86_exception *fault);
> -	bool (*hv_timer_pending)(struct kvm_vcpu *vcpu);
> +	bool (*has_events)(struct kvm_vcpu *vcpu);
>  	void (*triple_fault)(struct kvm_vcpu *vcpu);
>  	int (*get_state)(struct kvm_vcpu *vcpu,
>  			 struct kvm_nested_state __user *user_kvm_nested_state,
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index ddd4367d4826..9631cdcdd058 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3876,6 +3876,13 @@ static bool nested_vmx_preemption_timer_pending(struct kvm_vcpu *vcpu)
>  	       to_vmx(vcpu)->nested.preemption_timer_expired;
>  }
>  
> +static bool vmx_has_nested_events(struct kvm_vcpu *vcpu)
> +{
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> +	return nested_vmx_preemption_timer_pending(vcpu) || vmx->nested.mtf_pending;

How about:

	return nested_vmx_preemption_timer_pending(vcpu) ||
	       to_vmx(vcpu)->nested.mtf_pending;

to use less lines and honor the 80 char soft-limit?