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

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Date:   Mon, 11 Jun 2018 13:39:39 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        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, peterz@...radead.org,
        mathieu.poirier@...aro.org, kstewart@...uxfoundation.org,
        gregkh@...uxfoundation.org, rkrcmar@...hat.com, david@...hat.com,
        bsd@...hat.com, yu.c.zhang@...ux.intel.com, joro@...tes.org
Subject: Re: [PATCH v9 06/12] KVM: x86: Add Intel Processor Trace
 virtualization mode

On 07/06/2018 15:26, Alexander Shishkin wrote:
>> 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.

That is a superset of this choice:

a. hide PT from guests completely (the "a" above)

b. host-guest with guest preference: same as "b" above

c. host-guest with host preference: trace host/guest simultaneously, but
drop guest events if the host has tracing enabled.

so I don't think this choice is an issue.

Paolo