linux-kernel - [PATCH for 2.6.23] [1/3] x86_64: Add missing mask operation to vdso

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Message-Id: <20070911120210.0CFFC14EEC@wotan.suse.de>
Date:	Tue, 11 Sep 2007 14:02:09 +0200 (CEST)
From:	Andi Kleen <ak@...e.de>
To:	cebbert@...hat.com, torvalds@...l.org, patches@...-64.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH for 2.6.23] [1/3] x86_64: Add missing mask operation to vdso


vdso vgetns() didn't mask the time source offset calculation, which could
lead to time problems with 32bit HPET. Add the masking.

Thanks to Chuck Ebbert for tracking down.

Cc: cebbert@...hat.com

Signed-off-by: Andi Kleen <ak@...e.de>

Index: linux/arch/x86_64/vdso/vclock_gettime.c
===================================================================
--- linux.orig/arch/x86_64/vdso/vclock_gettime.c
+++ linux/arch/x86_64/vdso/vclock_gettime.c
@@ -34,10 +34,11 @@ static long vdso_fallback_gettime(long c
 
 static inline long vgetns(void)
 {
+	long v;
 	cycles_t (*vread)(void);
 	vread = gtod->clock.vread;
-	return ((vread() - gtod->clock.cycle_last) * gtod->clock.mult) >>
-		gtod->clock.shift;
+	v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
+	return (v * gtod->clock.mult) >> gtod->clock.shift;
 }
 
 static noinline int do_realtime(struct timespec *ts)
-
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