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: <20180503105032.h73n5lcrwkdbahgm@um.fi.intel.com>
Date:   Thu, 3 May 2018 13:50:32 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Luwei Kang <luwei.kang@...el.com>
Cc:     kvm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, pbonzini@...hat.com,
        rkrcmar@...hat.com, linux-kernel@...r.kernel.org, joro@...tes.org,
        peterz@...radead.org, 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 Thu, May 03, 2018 at 08:08:35PM +0800, Luwei Kang 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?

> diff --git a/arch/x86/include/asm/intel_pt.h b/arch/x86/include/asm/intel_pt.h
> index 2de4db0..3a4f524 100644
> --- a/arch/x86/include/asm/intel_pt.h
> +++ b/arch/x86/include/asm/intel_pt.h
> @@ -27,9 +27,11 @@ enum pt_capabilities {
>  #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
>  void cpu_emergency_stop_pt(void);
>  extern u32 pt_cap_get(enum pt_capabilities cap);
> +extern u32 __pt_cap_get(u32 *caps, enum pt_capabilities cap);

I'd call it something like pt_cap_decode().