linux-kernel - RE: [patch v2 8/8] KVM: x86: Disable intercept for Intel processor trace MSRs

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Message-ID: <82D7661F83C1A047AF7DC287873BF1E167E37591@SHSMSX101.ccr.corp.intel.com>
Date:   Tue, 14 Nov 2017 07:01:53 +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 v2 8/8] KVM: x86: Disable intercept for Intel processor
 trace MSRs

> > +	if (pt_mode == PT_MODE_HOST_GUEST) {
> > +		u32 i, eax, ebx, ecx, edx;
> > +
> > +		cpuid_count(0x14, 1, &eax, &ebx, &ecx, &edx);
> > +		vmx_disable_intercept_for_msr(MSR_IA32_RTIT_STATUS, false);
> > +		vmx_disable_intercept_for_msr(MSR_IA32_RTIT_OUTPUT_BASE, false);
> > +		vmx_disable_intercept_for_msr(MSR_IA32_RTIT_OUTPUT_MASK, false);
> > +		vmx_disable_intercept_for_msr(MSR_IA32_RTIT_CR3_MATCH, false);
> > +		for (i = 0; i < (eax & 0x7); i++)
> > +			vmx_disable_intercept_for_msr(MSR_IA32_RTIT_ADDR0_A + i,
> > +									false);
> > +	}
> > +
> 
> As I mentioned earlier, this probably makes vmentry/vmexit too expensive when guests are not using processor tracing.  I would do  it only if guest TRACEEN=1 (since anyway the values have to be correct if guest TRACEEN=1, and a change in TRACEEN always causes a vmexit).
> 

Will change in next version.

Thanks,
Luwei Kang

> 
> >  	return alloc_kvm_area();
> >
> >  out:
> >