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From:   "Kang, Luwei" <luwei.kang@intel.com>
To:     Alexander Shishkin <alexander.shishkin@linux.intel.com>
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Subject: RE: [PATCH v7 05/13] perf/x86/intel/pt: Introduce a new function to
 get capability of Intel PT
Thread-Topic: [PATCH v7 05/13] perf/x86/intel/pt: Introduce a new function
 to get capability of Intel PT
Thread-Index: AQHT4sefaepgQr78WUqju+HNtlv5nqQdTXEAgACIG+D//47xgIAAiXYQ
Date:   Thu, 3 May 2018 12:30:44 +0000
Message-ID: <82D7661F83C1A047AF7DC287873BF1E167F6DFFA@SHSMSX101.ccr.corp.intel.com>
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 <1525349323-9938-6-git-send-email-luwei.kang@intel.com>
 <20180503105032.h73n5lcrwkdbahgm@um.fi.intel.com>
 <82D7661F83C1A047AF7DC287873BF1E167F6DDCE@SHSMSX101.ccr.corp.intel.com>
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> > > > New function __pt_cap_get() will be invoked in KVM to check if a
> > > > specific capability is availiable in KVM guest.
> > > > Another function pt_cap_get() can only check the hardware
> > > > capabilities but this may different with KVM guest because some
> > > > features may not be exposed to guest.
> > >
> > > Do we really need both in KVM?
> >
> > Yes, KVM need get host capability to estimate if can expose this
> > feature to guest
> 
> Can you elaborate on this, what information do we need besides MSR_IA32_VMX_MISC[14]?

Enable Intel PT in guest depend on SECONDARY_EXEC_PT_USE_GPA, EPT, MSR_IA32_VMX_MISC[14] and the capability of " PT_CAP_topa_output" on hardware. PT driver will return " -ENODEV" if hardware not support "PT_CAP_topa_output".

Thanks,
Luwei Kang

> 
> Thanks,
> --
> Alex