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List:       kvm
Subject:    RE: [PATCH v1 8/8] perf/x86: Add event owner check when PEBS output to Intel PT
From:       "Kang, Luwei" <luwei.kang () intel ! com>
Date:       2019-10-31 10:31:20
Message-ID: 82D7661F83C1A047AF7DC287873BF1E1738363E9 () SHSMSX104 ! ccr ! corp ! intel ! com
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> > > Then how does KVM deal with the host using PT? You can't just steal PT.
> > 
> > Intel PT in virtualization can work in system and host_guest mode.
> > In system mode (default), the trace produced by host and guest will be saved in \
> > host PT buffer. Intel PT will not be exposed to guest
> in this mode.
> > In host_guest mode, Intel PT will be exposed to guest and guest can use PT like \
> > native. The value of host PT register will be saved
> and guest PT register value will be restored during VM-entry. Both trace of host \
> and guest are exported to their respective PT buffer. The host PT buffer not \
> include guest trace in this mode. 
> IOW, it will steal PT from the host.

Hi Alexander,
    The host buffer does not include guest packets in this mode because the guest \
trace will be saved in guest PT buffer in this mode. You can think it is stealing. 

> 
> Regards,
> --
> Alex


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