linux-kernel - [PATCH 1/5] x86/pvclock: make sure rdtsc doesn't speculate out of region

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Date:	Mon,  5 Oct 2009 17:50:07 -0700
From:	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
To:	Xen-devel <xen-devel@...ts.xensource.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kurt.hackel@...cle.com,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Keir Fraser <keir.fraser@...citrix.com>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Chris Mason <chris.mason@...cle.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: [PATCH 1/5] x86/pvclock: make sure rdtsc doesn't speculate out of region

rdtsc is not necessarily ordered with surrounding instructions so we
need to make sure that it doesn't get sampled out of order with
respect to reading the time_info.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/kernel/pvclock.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 03801f2..963f349 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -117,10 +117,10 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 
 	do {
 		version = pvclock_get_time_values(&shadow, src);
-		barrier();
+		rdtsc_barrier();
 		offset = pvclock_get_nsec_offset(&shadow);
 		ret = shadow.system_timestamp + offset;
-		barrier();
+		rdtsc_barrier();
 	} while (version != src->version);
 
 	return ret;
-- 
1.6.2.5

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