linux-kernel - [PATCH] RDMSR before test_cpu_capacity brings about KVM warning

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Date:	Fri, 14 Aug 2015 18:07:37 +0800
From:	Huaitong Han <huaitong.han@...el.com>
To:	alexander.shishkin@...ux.intel.com, mingo@...hat.com,
	acme@...nel.org
Cc:	linux-kernel@...r.kernel.org, Huaitong Han <huaitong.han@...el.com>
Subject: [PATCH] RDMSR before test_cpu_capacity brings about KVM warning

rdmsrl_safe does not lead to #GP in native kernel although CPU
does not support INTEL_PT, but if KVM does not support INTEL_PT,
the codes cannot understand MSR_IA32_RTIT_CTL, and the warning
is produced.

If KVM does not support INTEL_PT, its guest CPUID also does not.
So test_cpu_cap is added before RDMSR, and it is more in line with
the code style.

Signed-off-by: Huaitong Han <huaitong.han@...el.com>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index 183de71..4cc6492 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -123,9 +123,6 @@ 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,
@@ -1061,6 +1058,10 @@ 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;
-- 
1.9.1

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