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Subject: Re: [PATCH v9 06/12] KVM: x86: Add Intel Processor Trace
 virtualization mode
To:     Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Luwei Kang <luwei.kang@intel.com>
Cc:     kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, x86@kernel.org, chao.p.peng@linux.intel.com,
        thomas.lendacky@amd.com, bp@suse.de, Kan.liang@intel.com,
        Janakarajan.Natarajan@amd.com, dwmw@amazon.co.uk,
        linux-kernel@vger.kernel.org, peterz@infradead.org,
        mathieu.poirier@linaro.org, kstewart@linuxfoundation.org,
        gregkh@linuxfoundation.org, rkrcmar@redhat.com, david@redhat.com,
        bsd@redhat.com, yu.c.zhang@linux.intel.com, joro@8bytes.org
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 <1526964735-16566-7-git-send-email-luwei.kang@intel.com>
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From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Mon, 11 Jun 2018 13:39:39 +0200
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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