linux-kernel - [tip:x86/timers] x86/tsc: Use X86_FEATURE_TSC_ADJUST in detect

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Message-ID: <tip-7b3d2f6e08ed5eb6bcf6912938f7a542405f8e8e@git.kernel.org>
Date:   Tue, 29 Nov 2016 10:28:02 -0800
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     yinghai@...nel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, peterz@...radead.org, hpa@...or.com,
        mingo@...nel.org, bp@...en8.de
Subject: [tip:x86/timers] x86/tsc: Use X86_FEATURE_TSC_ADJUST in
 detect_art()

Commit-ID:  7b3d2f6e08ed5eb6bcf6912938f7a542405f8e8e
Gitweb:     http://git.kernel.org/tip/7b3d2f6e08ed5eb6bcf6912938f7a542405f8e8e
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sat, 19 Nov 2016 13:47:33 +0000
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 29 Nov 2016 19:23:15 +0100

x86/tsc: Use X86_FEATURE_TSC_ADJUST in detect_art()

The art detection uses rdmsrl_safe() to detect the availablity of the
TSC_ADJUST MSR.

That's pointless because we have a feature bit for this. Use it.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Yinghai Lu <yinghai@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Link: http://lkml.kernel.org/r/20161119134017.483561692@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/kernel/tsc.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 0ff1ec6..2b27c5a 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1057,18 +1057,20 @@ static void detect_art(void)
 	if (boot_cpu_data.cpuid_level < ART_CPUID_LEAF)
 		return;
 
-	cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator,
-	      &art_to_tsc_numerator, unused, unused+1);
-
-	/* Don't enable ART in a VM, non-stop TSC required */
+	/* Don't enable ART in a VM, non-stop TSC and TSC_ADJUST required */
 	if (boot_cpu_has(X86_FEATURE_HYPERVISOR) ||
 	    !boot_cpu_has(X86_FEATURE_NONSTOP_TSC) ||
-	    art_to_tsc_denominator < ART_MIN_DENOMINATOR)
+	    !boot_cpu_has(X86_FEATURE_TSC_ADJUST))
 		return;
 
-	if (rdmsrl_safe(MSR_IA32_TSC_ADJUST, &art_to_tsc_offset))
+	cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator,
+	      &art_to_tsc_numerator, unused, unused+1);
+
+	if (art_to_tsc_denominator < ART_MIN_DENOMINATOR)
 		return;
 
+	rdmsrl(MSR_IA32_TSC_ADJUST, art_to_tsc_offset);
+
 	/* Make this sticky over multiple CPU init calls */
 	setup_force_cpu_cap(X86_FEATURE_ART);
 }