From: Ingo Molnar <mingo@elte.hu>
Date: Sat, 8 Nov 2008 19:27:00 +0000 (+0100)
Subject: x86: clean up rdtsc_barrier() use
X-Git-Tag: v2.6.29-rc1~536^2~51
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=cb9e35dce94a1b9c59d46224e8a94377d673e204;p=karo-tx-linux.git

x86: clean up rdtsc_barrier() use

Impact: cleanup

Move rdtsc_barrier() use to vsyscall_64.c where it's relied on,
and point out its role in the context of its use.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 9cd83a8e40d5..700aeb8d2098 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -44,11 +44,7 @@ static __always_inline cycles_t vget_cycles(void)
 	if (!cpu_has_tsc)
 		return 0;
 #endif
-	rdtsc_barrier();
-	cycles = (cycles_t)__native_read_tsc();
-	rdtsc_barrier();
-
-	return cycles;
+	return (cycles_t)__native_read_tsc();
 }
 
 extern void tsc_init(void);
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 0b8b6690a86d..ebf2f12900f5 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -128,7 +128,16 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)
 			gettimeofday(tv,NULL);
 			return;
 		}
+
+		/*
+		 * Surround the RDTSC by barriers, to make sure it's not
+		 * speculated to outside the seqlock critical section and
+		 * does not cause time warps:
+		 */
+		rdtsc_barrier();
 		now = vread();
+		rdtsc_barrier();
+
 		base = __vsyscall_gtod_data.clock.cycle_last;
 		mask = __vsyscall_gtod_data.clock.mask;
 		mult = __vsyscall_gtod_data.clock.mult;