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: <7fd90c5d-ed6c-6156-1317-7a6767c99631@redhat.com>
Date:   Thu, 3 May 2018 14:30:15 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "Kang, Luwei" <luwei.kang@...el.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>,
        "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

On 03/05/2018 14:13, Alexander Shishkin wrote:
>>>> 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]?

It needs all the CPUID data, and it's nice to query it in a more
manageable form than with bit shifts.

Paolo