linux-kernel - Re: [PATCH v2 3/5] x86: KVM: clear interrupt shadow on EMULTYPE

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Message-ID: <20190806154539.GE27766@linux.intel.com>
Date:   Tue, 6 Aug 2019 08:45:39 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v2 3/5] x86: KVM: clear interrupt shadow on EMULTYPE_SKIP

On Tue, Aug 06, 2019 at 08:01:48AM +0200, Vitaly Kuznetsov wrote:
> When doing x86_emulate_instruction(EMULTYPE_SKIP) interrupt shadow has to
> be cleared if and only if the skipping is successful.
> 
> There are two immediate issues:
> - In SVM skip_emulated_instruction() we are not zapping interrupt shadow
>   in case kvm_emulate_instruction(EMULTYPE_SKIP) is used to advance RIP
>   (!nrpip_save).
> - In VMX handle_ept_misconfig() when running as a nested hypervisor we
>   (static_cpu_has(X86_FEATURE_HYPERVISOR) case) we forget to clear

Redundant 'we'.  Might be worth adding a blurb in the changelog to note
that this intentionally doesn't handle "MOV/POP SS" as skip-emulation of
those instructions can only occur if the guest is doing something silly.

Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>

>   interrupt shadow.
> 
> Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c6d951cbd76c..eac8253d84d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6537,6 +6537,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
>  		kvm_rip_write(vcpu, ctxt->_eip);
>  		if (ctxt->eflags & X86_EFLAGS_RF)
>  			kvm_set_rflags(vcpu, ctxt->eflags & ~X86_EFLAGS_RF);
> +		kvm_x86_ops->set_interrupt_shadow(vcpu, 0);
>  		return EMULATE_DONE;
>  	}
>  
> -- 
> 2.20.1
>