linux-kernel - RE: [PATCH v9 06/12] KVM: x86: Add Intel Processor Trace virtualization mode

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Message-ID: <82D7661F83C1A047AF7DC287873BF1E167FEFF92@SHSMSX101.ccr.corp.intel.com>
Date:   Fri, 8 Jun 2018 14:19:09 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "bp@...e.de" <bp@...e.de>, "Liang, Kan" <kan.liang@...el.com>,
        "Janakarajan.Natarajan@....com" <Janakarajan.Natarajan@....com>,
        "dwmw@...zon.co.uk" <dwmw@...zon.co.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mathieu.poirier@...aro.org" <mathieu.poirier@...aro.org>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "david@...hat.com" <david@...hat.com>,
        "bsd@...hat.com" <bsd@...hat.com>,
        "yu.c.zhang@...ux.intel.com" <yu.c.zhang@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>
Subject: RE: [PATCH v9 06/12] KVM: x86: Add Intel Processor Trace
 virtualization mode

> > From: Chao Peng <chao.p.peng@...ux.intel.com>
> >
> > Intel PT virtualization can be work in one of 2 possible modes:
> > a. system-wide: trace both host and guest and output to host buffer;
> > b. host-guest: trace host/guest simultaneous and output to their
> >    respective buffer.
> 
> I think we discussed this before. That's not the choice that the user needs to
> make. The only choice that I see is what happens if the guest wants to use PT
> while it's already in use by the host. Otherwise, each of them gets to use PT
> as they would.
> 

Hi,
    Thanks for your reply first. If guest want to use PT that we need to expose this feature to guest and guest will save these trace packets to guest buffer. Host will can't get the trace which are made by KVM guest. This is Host_Guest mode.
On the other hand,  host may also want to trace hypervisor and KVM guest execution trace and output these trace in native. This is SYSTEM mode. PT can't be exposed to guest in this mode or KVM guest trace will be lost in native buffer.
These are two different use case and can't coexist.

Thanks,
Luwei Kang