linux-kernel - Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode

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Date:   Fri, 4 May 2018 23:44:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Luwei Kang <luwei.kang@...el.com>, kvm@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, rkrcmar@...hat.com, linux-kernel@...r.kernel.org,
        joro@...tes.org, chao.p.peng@...ux.intel.com
Subject: Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace
 virtualization mode

On 04/05/2018 12:45, Peter Zijlstra wrote:
> On Thu, May 03, 2018 at 04:38:23PM +0300, Alexander Shishkin wrote:
>> On Thu, May 03, 2018 at 02:50:12PM +0200, Paolo Bonzini wrote:
> 
>>> And you still need the module parameter to decide
>>> whether the host is _allowed_ to cause incomplete traces in the guest.
>>
>> Or rather a parameter to decide who wins in case both host and guest want
>> to trace the guest. That's arguably better than having different versions of
>> PT in the guest depending on a module parameter setting.
> 
> Yes, that sounds like a much better approach.

I don't think so.  The possibility that the host would lose tracing data
just because the guest starts using PT seems hideous to me...

Paolo