linux-kernel - [PATCH 06/12] x86/pvclock: make sure rdtsc doesn't speculate out of region

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Message-Id: <1255548516-15260-7-git-send-email-jeremy.fitzhardinge@citrix.com>
Date:	Wed, 14 Oct 2009 12:28:30 -0700
From:	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Xen-devel <xen-devel@...ts.xensource.com>, kurt.hackel@...cle.com,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Chris Mason <chris.mason@...cle.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Ingo Molnar <mingo@...e.hu>, Gerd Hoffmann <kraxel@...hat.com>
Subject: [PATCH 06/12] 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>
Cc: Avi Kivity <avi@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Glauber Costa <gcosta@...hat.com>
Cc: Gerd Hoffmann <kraxel@...hat.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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