[RFC Patch 1/2][Bugfix][x86][hw-breakpoint] Clear reserved bits ofDR6 in do_debug()

[K.Prasad]

Clear the reserved bits from the stored copy of debug status register (DR6).
This will help easy bitwise operations.

Signed-off-by: K.Prasad <prasad@xxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/debugreg.h |    3 +++
 arch/x86/kernel/traps.c         |    3 +++
 2 files changed, 6 insertions(+)

Index: linux-2.6-tip/arch/x86/include/asm/debugreg.h
===================================================================
--- linux-2.6-tip.orig/arch/x86/include/asm/debugreg.h
+++ linux-2.6-tip/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 */
Index: linux-2.6-tip/arch/x86/kernel/traps.c
===================================================================
--- linux-2.6-tip.orig/arch/x86/kernel/traps.c
+++ linux-2.6-tip/arch/x86/kernel/traps.c
@@ -534,6 +534,9 @@ dotraplinkage void __kprobes do_debug(st
 
 	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;

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