linux-kernel - Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

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Date:   Tue, 21 Mar 2017 20:45:46 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     linux-kernel@...r.kernel.org,
        "Gabriel L. Somlo" <gsomlo@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

On Tue, Mar 21, 2017 at 05:16:32PM +0100, Joerg Roedel wrote:
> On Wed, Mar 15, 2017 at 11:22:18PM +0200, Michael S. Tsirkin wrote:
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index d1efe2c..18e53bc 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -1198,8 +1198,6 @@ static void init_vmcb(struct vcpu_svm *svm)
> >  	set_intercept(svm, INTERCEPT_CLGI);
> >  	set_intercept(svm, INTERCEPT_SKINIT);
> >  	set_intercept(svm, INTERCEPT_WBINVD);
> > -	set_intercept(svm, INTERCEPT_MONITOR);
> > -	set_intercept(svm, INTERCEPT_MWAIT);
> 
> Why do you remove the intercepts for AMD? The new kvm_mwait_in_guest()
> function will always return false on AMD anyway,

I think that's a bug and I should fix it to return true there.

> and on Intel you re-add
> the intercepts for !kvm_mwait_in_guest().
> 
> 
> 	Joerg

Does AMD need some work-around similar to CPUID5_ECX_INTERRUPT_BREAK?
That's why we have kvm_mwait_in_guest ...

-- 
MST