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Subject: Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace
 virtualization mode
To:     Peter Zijlstra <peterz@infradead.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc:     Luwei Kang <luwei.kang@intel.com>, kvm@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
        x86@kernel.org, rkrcmar@redhat.com, linux-kernel@vger.kernel.org,
        joro@8bytes.org, chao.p.peng@linux.intel.com
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 <221c297b-1270-371b-70a3-4cff4bed7a7e@redhat.com>
 <20180503124847.tcrizs2sxy3j6mu2@um.fi.intel.com>
 <26505f7a-9e6b-efb9-e5f9-8aae3756be49@redhat.com>
 <20180503133823.tqbraql3b7ltuo6a@um.fi.intel.com>
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From:   Paolo Bonzini <pbonzini@redhat.com>
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Message-ID: <10307518-a095-1a9d-d488-58db88fe16bd@redhat.com>
Date:   Fri, 4 May 2018 23:44:09 +0200
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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