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Subject[tip:x86/timers] x86/tsc: Use X86_FEATURE_TSC_ADJUST in detect_art()
Commit-ID:  67693acebe8c90ec93703b610d9622134249646a
Gitweb: http://git.kernel.org/tip/67693acebe8c90ec93703b610d9622134249646a
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Sat, 19 Nov 2016 13:47:33 +0000
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 29 Nov 2016 17:29:46 +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@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/20161119134017.483561692@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.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);
}
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