[PATCH v2 2/2] x86/hw_breakpoint: Add arch_reinstall_hw_breakpoint

[Jinchao Wang <wangjinchao600@gmail.com>]

The new arch_reinstall_hw_breakpoint() function can be used in an
atomic context, unlike the more expensive free and re-allocation path.
This allows callers to efficiently re-establish an existing breakpoint.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 arch/x86/include/asm/hw_breakpoint.h | 2 ++
 arch/x86/kernel/hw_breakpoint.c      | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h
index aa6adac6c3a2..c22cc4e87fc5 100644
--- a/arch/x86/include/asm/hw_breakpoint.h
+++ b/arch/x86/include/asm/hw_breakpoint.h
@@ -21,6 +21,7 @@ struct arch_hw_breakpoint {
 
 enum bp_slot_action {
 	BP_SLOT_ACTION_INSTALL,
+	BP_SLOT_ACTION_REINSTALL,
 	BP_SLOT_ACTION_UNINSTALL,
 };
 
@@ -65,6 +66,7 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 
 
 int arch_install_hw_breakpoint(struct perf_event *bp);
+int arch_reinstall_hw_breakpoint(struct perf_event *bp);
 void arch_uninstall_hw_breakpoint(struct perf_event *bp);
 void hw_breakpoint_pmu_read(struct perf_event *bp);
 void hw_breakpoint_pmu_unthrottle(struct perf_event *bp);
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 3658ace4bd8d..29c9369264d4 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -99,6 +99,10 @@ static int manage_bp_slot(struct perf_event *bp, enum bp_slot_action action)
 		old_bp = NULL;
 		new_bp = bp;
 		break;
+	case BP_SLOT_ACTION_REINSTALL:
+		old_bp = bp;
+		new_bp = bp;
+		break;
 	case BP_SLOT_ACTION_UNINSTALL:
 		old_bp = bp;
 		new_bp = NULL;
@@ -187,6 +191,11 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
 	return arch_manage_bp(bp, BP_SLOT_ACTION_INSTALL);
 }
 
+int arch_reinstall_hw_breakpoint(struct perf_event *bp)
+{
+	return arch_manage_bp(bp, BP_SLOT_ACTION_REINSTALL);
+}
+
 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
 {
 	arch_manage_bp(bp, BP_SLOT_ACTION_UNINSTALL);
-- 
2.43.0