[Patch 2/2 v2] Return proper code to notifier chain in hw_breakpoint_handler

[K.Prasad]

[K.Prasad]

[tip-bot for K.Prasad]

Commit-ID: e0e53db6133c32964fd17f20b17073a402f07ed3
Gitweb: http://git.kernel.org/tip/e0e53db6133c32964fd17f20b17073a402f07ed3
Author: K.Prasad <pra...@linux.vnet.ibm.com>
AuthorDate: Thu, 28 Jan 2010 16:44:15 +0530
Committer: Frederic Weisbecker <fwei...@gmail.com>
CommitDate: Fri, 29 Jan 2010 02:44:30 +0100

x86/hw-breakpoints: Optimize return code from notifier chain in hw_breakpoint_handler

Processing of debug exceptions in do_debug() can stop if it
originated from a hw-breakpoint exception by returning NOTIFY_STOP
in most cases.

But for certain cases such as:

a) user-space breakpoints with pending SIGTRAP signal delivery (as
in the case of ptrace induced breakpoints).

b) exceptions due to other causes than breakpoints

We will continue to process the exception by returning NOTIFY_DONE.

Signed-off-by: K.Prasad <pra...@linux.vnet.ibm.com>
Cc: Ingo Molnar <mi...@elte.hu>
Cc: Roland McGrath <rol...@redhat.com>
Cc: Alan Stern <st...@rowland.harvard.edu>
Cc: Jan Kiszka <jan.k...@siemens.com>
LKML-Reference: <20100128111...@in.ibm.com>
Signed-off-by: Frederic Weisbecker <fwei...@gmail.com>
---
arch/x86/kernel/hw_breakpoint.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 05d5fec..ae90b47 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -502,8 +502,6 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args)
rcu_read_lock();

bp = per_cpu(bp_per_reg[i], cpu);
- if (bp)
- rc = NOTIFY_DONE;
/*
* Reset the 'i'th TRAP bit in dr6 to denote completion of
* exception handling
@@ -522,7 +520,13 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args)

rcu_read_unlock();
}
- if (dr6 & (~DR_TRAP_BITS))
+ /*
+ * Further processing in do_debug() is needed for a) user-space
+ * breakpoints (to generate signals) and b) when the system has
+ * taken exception due to multiple causes
+ */
+ if ((current->thread.debugreg6 & DR_TRAP_BITS) ||
+ (dr6 & (~DR_TRAP_BITS)))
rc = NOTIFY_DONE;

set_debugreg(dr7, 7);
--
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[tip-bot for K.Prasad]

Commit-ID: 40f9249a73f6c251adea492b1c3d19d39e2a9bda
Gitweb: http://git.kernel.org/tip/40f9249a73f6c251adea492b1c3d19d39e2a9bda
Author: K.Prasad <pra...@linux.vnet.ibm.com>
AuthorDate: Thu, 28 Jan 2010 16:44:01 +0530
Committer: Frederic Weisbecker <fwei...@gmail.com>
CommitDate: Fri, 29 Jan 2010 02:26:10 +0100

x86/debug: Clear reserved bits of DR6 in do_debug()

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 <pra...@linux.vnet.ibm.com>
Cc: Roland McGrath <rol...@redhat.com>
Cc: Jan Kiszka <jan.k...@siemens.com>
Cc: Alan Stern <st...@rowland.harvard.edu>
Cc: Ingo Molnar <mi...@elte.hu>

LKML-Reference: <20100128111...@in.ibm.com>
Signed-off-by: Frederic Weisbecker <fwei...@gmail.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;