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Date: Thu, 12 Nov 2015 12:06:44 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Borislav Petkov <bp@alien8.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] perf/x86/intel/pt: Test CPU vendor before loading
Message-ID: <20151112110644.GY17308@twins.programming.kicks-ass.net>
References: <1447325772-4799-1-git-send-email-bp@alien8.de>
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On Thu, Nov 12, 2015 at 11:56:12AM +0100, Borislav Petkov wrote:
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
> index 42169283448b..fa1262b025e7 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
> @@ -1129,6 +1129,9 @@ static __init int pt_init(void)
>  {
>  	int ret, cpu, prior_warn = 0;
>  
> +	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
> +		return 0;
> +

Does not apply; conflicts with:


commit 73fdeb66592ee80dffb16fb8a9b7378a00c1a826
Author: Huaitong Han <huaitong.han@intel.com>
Date:   Mon Aug 31 16:21:02 2015 +0800

    perf/x86/intel/pt: Fix KVM warning due to doing rdmsr() before the CPUID test
    
    If KVM does not support INTEL_PT, guest MSR_IA32_RTIT_CTL reading will
    produce host warning like "kvm [2469]: vcpu0 unhandled rdmsr: 0x570".
    
    Guest can determine whether the CPU supports Intel_PT according to CPUID,
    so test_cpu_cap function is added before rdmsr,and it is more in line with
    the code style.
    
    Signed-off-by: Huaitong Han <huaitong.han@intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Cc: acme@kernel.org
    Link: http://lkml.kernel.org/r/1441009262-9792-1-git-send-email-huaitong.han@intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index 42169283448b..868e1194337f 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -139,9 +139,6 @@ static int __init pt_pmu_hw_init(void)
 	long i;
 
 	attrs = NULL;
-	ret = -ENODEV;
-	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT))
-		goto fail;
 
 	for (i = 0; i < PT_CPUID_LEAVES; i++) {
 		cpuid_count(20, i,
@@ -1130,6 +1127,10 @@ static __init int pt_init(void)
 	int ret, cpu, prior_warn = 0;
 
 	BUILD_BUG_ON(sizeof(struct topa) > PAGE_SIZE);
+
+	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT))
+		return -ENODEV;
+
 	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		u64 ctl;