linux-kernel - Re: [PATCH v9 04/12] perf/x86/intel/pt: add new capability for Intel PT

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Date:   Thu, 7 Jun 2018 16:40:51 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Luwei Kang <luwei.kang@...el.com>
Cc:     kvm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, chao.p.peng@...ux.intel.com,
        thomas.lendacky@....com, bp@...e.de, Kan.liang@...el.com,
        Janakarajan.Natarajan@....com, dwmw@...zon.co.uk,
        linux-kernel@...r.kernel.org, alexander.shishkin@...ux.intel.com,
        peterz@...radead.org, mathieu.poirier@...aro.org,
        kstewart@...uxfoundation.org, gregkh@...uxfoundation.org,
        pbonzini@...hat.com, rkrcmar@...hat.com, david@...hat.com,
        bsd@...hat.com, yu.c.zhang@...ux.intel.com, joro@...tes.org
Subject: Re: [PATCH v9 04/12] perf/x86/intel/pt: add new capability for Intel
 PT

On Tue, May 22, 2018 at 12:52:07PM +0800, Luwei Kang wrote:
> CPUID(EAX=14H,ECX=0):EBX[bit 3] = 1 indicates support of
> output to Trace Transport subsystem.
> MSR IA32_RTIT_CTL.FabricEn[bit 6] is reserved if
> CPUID.(EAX=14H, ECX=0):ECX[bit 3] = 0.

This should instead say:

This adds support for "output to Trace Transport subsystem" capability
of Intel PT, as documented in IA SDM Chapter 36.x.y.z. It means that
PT can output its trace to an MMIO address range rather than system
memory buffer.

> This is use for emulate IA32_RTIT_CTL MSR read/write
> in KVM. KVM guest write IA32_RTIT_CTL will trap to
> root mode and a #GP would be injected to guest if set
> IA32_RTIT_CTL.FabricEn with
> CPUID.(EAX=14H, ECX=0):ECX[bit 3] = 0.

I'm not sure what this means, this patch has nothing to do with KVM
as far as I can tell.

Aside from the commit message, this is a valid patch.

Thanks,
--
Alex