linux-kernel - [PATCH 4/5] x86/debug: Clear reserved bits of DR6 in do

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Message-Id: <1264730829-14563-5-git-send-regression-fweisbec@gmail.com>
Date:	Fri, 29 Jan 2010 03:07:08 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 4/5] x86/debug: Clear reserved bits of DR6 in do_debug()

From: K.Prasad <prasad@...ux.vnet.ibm.com>

Clear the reserved bits from the stored copy of debug status
register (DR6).
This will help easy bitwise operations such as quick testing
of a debug event origin.

Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com>
Cc: Roland McGrath <roland@...hat.com>
Cc: Jan Kiszka <jan.kiszka@...mens.com>
Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Ingo Molnar <mingo@...e.hu>
LKML-Reference: <20100128111401.GB13935@...ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 arch/x86/include/asm/debugreg.h |    3 +++
 arch/x86/kernel/traps.c         |    3 +++
 2 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h
index 8240f76..b81002f 100644
--- a/arch/x86/include/asm/debugreg.h
+++ b/arch/x86/include/asm/debugreg.h
@@ -14,6 +14,9 @@
    which debugging register was responsible for the trap.  The other bits
    are either reserved or not of interest to us. */
 
+/* Define reserved bits in DR6 which are always set to 1 */
+#define DR6_RESERVED	(0xFFFF0FF0)
+
 #define DR_TRAP0	(0x1)		/* db0 */
 #define DR_TRAP1	(0x2)		/* db1 */
 #define DR_TRAP2	(0x4)		/* db2 */
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3339917..1168e44 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -534,6 +534,9 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 
 	get_debugreg(dr6, 6);
 
+	/* Filter out all the reserved bits which are preset to 1 */
+	dr6 &= ~DR6_RESERVED;
+
 	/* Catch kmemcheck conditions first of all! */
 	if ((dr6 & DR_STEP) && kmemcheck_trap(regs))
 		return;
-- 
1.6.2.3

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