commit 62edab9056a6cf0c9207339c8892c923a5217e45
author K.Prasad <prasad@linux.vnet.ibm.com> Mon Jun 01 23:47:06 2009 +0530
committer Frederic Weisbecker <fweisbec@gmail.com> Tue Jun 02 22:47:00 2009 +0200
tree 2becd775fdc2a25df3daacf69d80685b251fbed9
parent 0722db015c246204044299eae3b02d18d3ca4faf

hw-breakpoints: reset bits in dr6 after the corresponding exception is handled

This patch resets the bit in dr6 after the corresponding exception is
handled in code, so that we keep a clean track of the current virtual debug
status register.

[ Impact: keep track of breakpoints triggering completion ]

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

arch/x86/kernel/hw_breakpoint.c

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 4867c9f..6945147 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -314,8 +314,12 @@
 {
 	int i, cpu, rc = NOTIFY_STOP;
 	struct hw_breakpoint *bp;
-	/* The DR6 value is stored in args->err */
-	unsigned long dr7, dr6 = args->err;
+	unsigned long dr7, dr6;
+	unsigned long *dr6_p;
+
+	/* The DR6 value is pointed by args->err */
+	dr6_p = (unsigned long *)ERR_PTR(args->err);
+	dr6 = *dr6_p;
 
 	/* Do an early return if no trap bits are set in DR6 */
 	if ((dr6 & DR_TRAP_BITS) == 0)
@@ -352,6 +356,11 @@
 				rc = NOTIFY_DONE;
 		}
 		/*
+		 * Reset the 'i'th TRAP bit in dr6 to denote completion of
+		 * exception handling
+		 */
+		(*dr6_p) &= ~(DR_TRAP0 << i);
+		/*
 		 * bp can be NULL due to lazy debug register switching
 		 * or due to the delay between updates of hbp_kernel_pos
 		 * and this_hbp_kernel.

arch/x86/kernel/kgdb.c

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index b1f4dff..f820b73 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -43,6 +43,7 @@
 #include <linux/smp.h>
 #include <linux/nmi.h>
 
+#include <asm/debugreg.h>
 #include <asm/apicdef.h>
 #include <asm/system.h>
 
@@ -434,6 +435,11 @@
 			"resuming...\n");
 	kgdb_arch_handle_exception(args->trapnr, args->signr,
 				   args->err, "c", "", regs);
+	/*
+	 * Reset the BS bit in dr6 (pointed by args->err) to
+	 * denote completion of processing
+	 */
+	(*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
 
 	return NOTIFY_STOP;
 }

arch/x86/kernel/kprobes.c

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7b5169d..b5b1848 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -54,6 +54,7 @@
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
 #include <asm/alternative.h>
+#include <asm/debugreg.h>
 
 void jprobe_return_end(void);
 
@@ -967,8 +968,14 @@
 			ret = NOTIFY_STOP;
 		break;
 	case DIE_DEBUG:
-		if (post_kprobe_handler(args->regs))
+		if (post_kprobe_handler(args->regs)) {
+			/*
+			 * Reset the BS bit in dr6 (pointed by args->err) to
+			 * denote completion of processing
+			 */
+			(*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
 			ret = NOTIFY_STOP;
+		}
 		break;
 	case DIE_GPF:
 		/*

arch/x86/kernel/traps.c

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index de99132..124a4d5 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -545,8 +545,8 @@
 	/* Store the virtualized DR6 value */
 	tsk->thread.debugreg6 = dr6;
 
-	if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
-						SIGTRAP) == NOTIFY_STOP)
+	if (notify_die(DIE_DEBUG, "debug", regs, PTR_ERR(&dr6), error_code,
+							SIGTRAP) == NOTIFY_STOP)
 		return;
 
 	/* It's safe to allow irq's after DR6 has been saved */