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>

1 files changed, 11 insertions, 2 deletions

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 4867c9f3b5fb..69451473dbd2 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -314,8 +314,12 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
 {
         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 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
                                 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.