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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     linmiaohe <linmiaohe@huawei.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org,
        pbonzini@redhat.com, rkrcmar@redhat.com,
        sean.j.christopherson@intel.com, wanpengli@tencent.com,
        jmattson@google.com, joro@8bytes.org, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com
Subject: Re: [PATCH] KVM: nVMX: set rflags to specify success in handle_invvpid() default case
In-Reply-To: <1579749241-712-1-git-send-email-linmiaohe@huawei.com>
References: <1579749241-712-1-git-send-email-linmiaohe@huawei.com>
Date:   Thu, 23 Jan 2020 09:55:44 +0100
Message-ID: <8736c6sga7.fsf@vitty.brq.redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org
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linmiaohe <linmiaohe@huawei.com> writes:

> From: Miaohe Lin <linmiaohe@huawei.com>
>
> In handle_invvpid() default case, we just skip emulated instruction and
> forget to set rflags to specify success. This would result in indefinite
> rflags value and thus indeterminate return value for guest.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> 	Chinese New Year is coming. Happy Spring Festival! ^_^

Happy Spring Festival!

> ---
>  arch/x86/kvm/vmx/nested.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 7608924ee8c1..985d3307ec56 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5165,7 +5165,7 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
>  		break;
>  	default:
>  		WARN_ON_ONCE(1);
> -		return kvm_skip_emulated_instruction(vcpu);
> +		break;
>  	}
>  
>  	return nested_vmx_succeed(vcpu);

Your patch seems to do the right thing, however, I started wondering if
WARN_ON_ONCE() is the right thing to do. SDM says that "If an
unsupported INVVPID type is specified, the instruction fails." and this
is similar to INVEPT and I decided to check what handle_invept()
does. Well, it does BUG_ON(). 

Are we doing the right thing in any of these cases?

-- 
Vitaly