linux-kernel - [PATCH v3 07/18] x86/cpu/amd: Use the full 64-bit TSC to detect the 2.6.2 bug

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Message-Id: <d58f339a9c0dd8352b50d2f7a216f67ec2844f20.1434501121.git.luto@kernel.org>
Date:	Tue, 16 Jun 2015 17:35:55 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	Borislav Petkov <bp@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	Huang Rui <ray.huang@....com>,
	Denys Vlasenko <dvlasenk@...hat.com>, kvm@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v3 07/18] x86/cpu/amd: Use the full 64-bit TSC to detect the 2.6.2 bug

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>
---
 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 5bd3a99dc20b..c5ceec532799 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -107,7 +107,7 @@ 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 - ");
 
@@ -118,10 +118,10 @@ 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)
-- 
2.4.2

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