[Patch 4/4] PPC64-HWBKPT: Enable hw-breakpoints while handling intervening signals

["K.Prasad" <prasad@linux.vnet.ibm.com>]

A signal delivered between a hw_breakpoint_handler() and the
single_step_dabr_instruction() will not have the breakpoint active during
signal handling (since breakpoint will not be restored through single-stepping
due to absence of MSR_SE bit on the signal frame). Enable breakpoints before
signal delivery.

Restore hw-breakpoints if the user-context is altered in the signal handler.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/hw_breakpoint.h |    2 ++
 arch/powerpc/kernel/hw_breakpoint.c      |   16 ++++++++++++++++
 arch/powerpc/kernel/signal.c             |    3 +++
 arch/powerpc/kernel/signal_32.c          |    2 ++
 arch/powerpc/kernel/signal_64.c          |    2 ++
 5 files changed, 25 insertions(+)

Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/include/asm/hw_breakpoint.h
+++ linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h
@@ -65,9 +65,11 @@ static inline void hw_breakpoint_disable
 {
 	set_dabr(0);
 }
+extern void thread_change_pc(struct task_struct *tsk);
 
 #else	/* CONFIG_HAVE_HW_BREAKPOINT */
 static inline void hw_breakpoint_disable(void) { }
+static inline void thread_change_pc(struct task_struct *tsk) { }
 #endif	/* CONFIG_HAVE_HW_BREAKPOINT */
 #endif	/* __KERNEL__ */
 #endif	/* _PPC_BOOK3S_64_HW_BREAKPOINT_H */
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/hw_breakpoint.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
@@ -176,6 +176,22 @@ int arch_validate_hwbkpt_settings(struct
 }
 
 /*
+ * Restores the breakpoint on the debug registers.
+ * Invoke this function if it is known that the execution context is about to
+ * change to cause loss of MSR_SE settings.
+ */
+void thread_change_pc(struct task_struct *tsk)
+{
+	struct arch_hw_breakpoint *info;
+
+	if (likely(!tsk->thread.last_hit_ubp))
+		return;
+
+	info = counter_arch_bp(tsk->thread.last_hit_ubp);
+	set_dabr(info->address | info->type | DABR_TRANSLATION);
+}
+
+/*
  * Handle debug exception notifications.
  */
 int __kprobes hw_breakpoint_handler(struct die_args *args)
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/signal.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/signal.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/signal.c
@@ -11,6 +11,7 @@
 
 #include <linux/tracehook.h>
 #include <linux/signal.h>
+#include <asm/hw_breakpoint.h>
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 
@@ -149,6 +150,8 @@ static int do_signal_pending(sigset_t *o
 	if (current->thread.dabr)
 		set_dabr(current->thread.dabr);
 #endif
+	 /* Re-enable the breakpoints for the signal stack */
+	thread_change_pc(current);
 
 	if (is32) {
         	if (ka.sa.sa_flags & SA_SIGINFO)
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/signal_64.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/signal_64.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/signal_64.c
@@ -33,6 +33,7 @@
 #include <asm/cacheflush.h>
 #include <asm/syscalls.h>
 #include <asm/vdso.h>
+#include <asm/hw_breakpoint.h>
 
 #include "signal.h"
 
@@ -312,6 +313,7 @@ int sys_swapcontext(struct ucontext __us
 		    || __copy_to_user(&old_ctx->uc_sigmask,
 				      &current->blocked, sizeof(sigset_t)))
 			return -EFAULT;
+		thread_change_pc(current);
 	}
 	if (new_ctx == NULL)
 		return 0;
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/signal_32.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/signal_32.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/signal_32.c
@@ -42,6 +42,7 @@
 #include <asm/syscalls.h>
 #include <asm/sigcontext.h>
 #include <asm/vdso.h>
+#include <asm/hw_breakpoint.h>
 #ifdef CONFIG_PPC64
 #include "ppc32.h"
 #include <asm/unistd.h>
@@ -996,6 +997,7 @@ long sys_swapcontext(struct ucontext __u
 		    || put_sigset_t(&old_ctx->uc_sigmask, &current->blocked)
 		    || __put_user(to_user_ptr(mctx), &old_ctx->uc_regs))
 			return -EFAULT;
+		thread_change_pc(current);
 	}
 	if (new_ctx == NULL)
 		return 0;