linux-kernel - RE: [PATCH 0/9] Intel Processor Trace virtulization enabling

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Date:   Wed, 18 Oct 2017 11:06:48 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Subject: RE: [PATCH 0/9] Intel Processor Trace virtulization enabling

> >> Nested virtualization is interesting.  We would like the nested
> >> hypervisor to be forced to set the "use GPA for processor tracing"
> >> secondary execution control whenever "enable EPT" is set and RTIT_CTL
> >> is nonzero.  There is no way to encode that in
> >> IA32_VMX_PROCBASED_CTLS2, however.  It would be nice if Intel could
> >> reserve a bit in IA32_VMX_EPT_VPID_CAP for KVM to express that
> >> constraint.
> >
> > Do you mean if nested hypervisor get the capability of "Guest PT use
> > GPA" and EPT has enable. Highly recommend nested hypervisor set "
> > Guest PT use GPA " as well.
> 
> Well, it's required more than recommended.  However, it's only required if "enable EPT" is set and RTIT_CTL is nonzero.
> 
> > If nested hypervisor is also KVM, "use GPA for processor tracing"
> > will be set for sure. But other hypervisor may not do that. So, we'd
> > better add a flag in IA32_VMX_EPT_VPID_CAP to express that constraint.
> 
> Correct.  The constraint would be:
> 
> * RTIT_CTL on entry is zero if EPT is disabled
> 
> * RTIT_CTL on entry is zero if EPT is enabled and "Guest PT uses GPA" is zero
> 
> Maybe IA32_VMX_EPT_VPID_CAP is not the best place.  I'll let Intel decide that.
> 

Get it. I have feedback to hardware architect. I hope it can be applied but it may need wait a long time.

Thanks,
Luwei Kang