linux-kernel - RE: [PATCH v7 05/13] perf/x86/intel/pt: Introduce a new function to get capability of Intel PT

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Message-ID: <82D7661F83C1A047AF7DC287873BF1E167F6DFFA@SHSMSX101.ccr.corp.intel.com>
Date:   Thu, 3 May 2018 12:30:44 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>
Subject: RE: [PATCH v7 05/13] perf/x86/intel/pt: Introduce a new function to
 get capability of Intel PT

> > > > 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