linux-kernel - Re: [PATCH 02/10] KVM: nVMX: Drop a superfluous WARN on reflecting EXTERNAL

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Message-ID: <87h7yspi34.fsf@vitty.brq.redhat.com>
Date:   Fri, 13 Mar 2020 13:14:39 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 02/10] KVM: nVMX: Drop a superfluous WARN on reflecting EXTERNAL_INTERRUPT

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Drop the WARN in nested_vmx_reflect_vmexit() that fires if KVM attempts
> to reflect an external interrupt.  nested_vmx_exit_reflected() is now
> called from nested_vmx_reflect_vmexit() and unconditionally returns
> false for EXTERNAL_INTERRUPT, i.e. barring a compiler or major CPU bug,
> the WARN will never fire.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/nested.h | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
> index 6bc379cf4755..8f5ff3e259c9 100644
> --- a/arch/x86/kvm/vmx/nested.h
> +++ b/arch/x86/kvm/vmx/nested.h
> @@ -84,12 +84,11 @@ static inline bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu,
>  		return false;
>  
>  	/*
> -	 * At this point, the exit interruption info in exit_intr_info
> -	 * is only valid for EXCEPTION_NMI exits.  For EXTERNAL_INTERRUPT
> -	 * we need to query the in-kernel LAPIC.
> +	 * vmcs.VM_EXIT_INTR_INFO is only valid for EXCEPTION_NMI exits.  For
> +	 * EXTERNAL_INTERRUPT, the value for vmcs12->vm_exit_intr_info would
> +	 * need to be synthesized by querying the in-kernel LAPIC, but external
> +	 * interrupts are never reflected to L1 so it's a non-issue.
>  	 */
> -	WARN_ON(exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT);
> -
>  	exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
>  	if ((exit_intr_info &
>  	     (INTR_INFO_VALID_MASK | INTR_INFO_DELIVER_CODE_MASK)) ==

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly