linux-kernel - Re: [RFC PATCH] perf: honouring the cpuid for number of fixed counters in hypervisors

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Message-ID: <20161016135039.GK3142@twins.programming.kicks-ass.net>
Date:   Sun, 16 Oct 2016 15:50:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Imre Palik <imrep.amz@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Kan Liang <kan.liang@...el.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Alexander Kozyrev <alexander.kozyrev@...el.com>,
        Artyom Kuanbekov <artyom.kuanbekov@...el.com>,
        Imre Palik <imrep@...zon.de>, Matt Wilson <msw@...zon.com>
Subject: Re: [RFC PATCH] perf: honouring the cpuid for number of fixed
 counters in hypervisors

On Thu, Oct 13, 2016 at 01:28:09AM -0700, Imre Palik wrote:
> +	if (version > 1) {
> +		unsigned int ecx = cpuid_ecx(1);
> +
> +		if (ecx >> 31)

What is this magic, undocumented gunk doing? Is that supposed to be
static_cpu_has(X86_FEATURE_HYPERVISOR) ?