linux-kernel - Re: [PATCH] KVM: x86: Exit to userspace when kvm_check_nested

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Message-ID: <YQGEoRTfGhinO41u@google.com>
Date:   Wed, 28 Jul 2021 16:24:01 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH] KVM: x86: Exit to userspace when kvm_check_nested_events
 fails

On Wed, Jul 28, 2021, Paolo Bonzini wrote:
> From: Jim Mattson <jmattson@...gle.com>

I don't think this is actually from Jim.

> If kvm_check_nested_events fails due to raising an
> EXIT_REASON_INTERNAL_ERROR, propagate it to userspace
> immediately, even if the vCPU would otherwise be sleeping.
> This happens for example when the posted interrupt descriptor
> points outside guest memory.
> 
> Reported-by: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 348452bb16bc..916c976e99ab 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9752,10 +9752,14 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
>  	return 1;
>  }
>  
> -static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
> +static inline int kvm_vcpu_running(struct kvm_vcpu *vcpu)
>  {
> -	if (is_guest_mode(vcpu))
> -		kvm_check_nested_events(vcpu);
> +	int r;

newline

> +	if (is_guest_mode(vcpu)) {
> +		r = kvm_check_nested_events(vcpu);
> +		if (r < 0 && r != -EBUSY)
> +			return r;
> +	}
>  
>  	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
>  		!vcpu->arch.apf.halted);
> @@ -9770,12 +9774,16 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
>  	vcpu->arch.l1tf_flush_l1d = true;
>  
>  	for (;;) {
> -		if (kvm_vcpu_running(vcpu)) {
> -			r = vcpu_enter_guest(vcpu);
> -		} else {
> -			r = vcpu_block(kvm, vcpu);
> +		r = kvm_vcpu_running(vcpu);
> +		if (r < 0) {
> +			r = 0;
> +			break;
>  		}
>  
> +		if (r)
> +			r = vcpu_enter_guest(vcpu);
> +		else
> +			r = vcpu_block(kvm, vcpu);
>  		if (r <= 0)
>  			break;
>  
> -- 
> 2.27.0
>