linux-kernel - [PATCH 07/19] x86/cpu/amd: Use the full 64-bit TSC to detect the 2.6.2 bug

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Date:	Thu, 25 Jun 2015 18:44:01 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 07/19] x86/cpu/amd: Use the full 64-bit TSC to detect the 2.6.2 bug

From: Andy Lutomirski <luto@...nel.org>

This code is timing 100k indirect calls, so the added overhead of
counting the number of cycles elapsed as a 64-bit number should be
insignificant.  Drop the optimization of using a 32-bit count.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Huang Rui <ray.huang@....com>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Len Brown <lenb@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: kvm ML <kvm@...r.kernel.org>
Cc: x86-ml <x86@...nel.org>
Link: http://lkml.kernel.org/r/d58f339a9c0dd8352b50d2f7a216f67ec2844f20.1434501121.git.luto@kernel.org
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/amd.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index dd3a4baffe50..a69710db6112 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -114,7 +114,7 @@ static void init_amd_k6(struct cpuinfo_x86 *c)
 		const int K6_BUG_LOOP = 1000000;
 		int n;
 		void (*f_vide)(void);
-		unsigned long d, d2;
+		u64 d, d2;
 
 		printk(KERN_INFO "AMD K6 stepping B detected - ");
 
@@ -125,10 +125,10 @@ static void init_amd_k6(struct cpuinfo_x86 *c)
 
 		n = K6_BUG_LOOP;
 		f_vide = vide;
-		rdtscl(d);
+		d = native_read_tsc();
 		while (n--)
 			f_vide();
-		rdtscl(d2);
+		d2 = native_read_tsc();
 		d = d2-d;
 
 		if (d > 20*K6_BUG_LOOP)
-- 
2.3.5

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