[PATCH 3/3] HWBP: Add modify_local_hw_breakpoint_addr() API

[Jinchao Wang]

From: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>

Add modify_local_hw_breakpoint_addr() to update only the watched
address of an installed hardware breakpoint on the local CPU without
releasing and reserving its hardware slot. This is available when the
architecture selects CONFIG_HAVE_MODIFY_LOCAL_HW_BREAKPOINT_ADDR.

The caller must provide an installed local event and a valid address,
and update other CPUs separately.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Jinchao Wang <wangjinchao600@xxxxxxxxx>
---
 arch/Kconfig                  |  8 ++++++++
 arch/x86/Kconfig              |  1 +
 include/linux/hw_breakpoint.h |  6 ++++++
 kernel/events/hw_breakpoint.c | 30 ++++++++++++++++++++++++++++++
 4 files changed, 45 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index fa7507ac8e13..bea383408e32 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -457,6 +457,14 @@ config HAVE_MIXED_BREAKPOINTS_REGS
 	  Select this option if your arch implements breakpoints under the
 	  latter fashion.
 
+config HAVE_MODIFY_LOCAL_HW_BREAKPOINT_ADDR
+	bool
+	depends on HAVE_HW_BREAKPOINT
+	help
+	  Select this if the architecture can modify the address of an
+	  installed hardware breakpoint on the local CPU without releasing
+	  and reserving its hardware slot.
+
 config HAVE_USER_RETURN_NOTIFIER
 	bool
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..09e599f2d0dd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -246,6 +246,7 @@ config X86
 	select HAVE_FUNCTION_TRACER
 	select HAVE_GCC_PLUGINS
 	select HAVE_HW_BREAKPOINT
+	select HAVE_MODIFY_LOCAL_HW_BREAKPOINT_ADDR
 	select HAVE_IOREMAP_PROT
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK	if X86_64
 	select HAVE_IRQ_TIME_ACCOUNTING
diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index db199d653dd1..bf65c7fffd99 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -81,6 +81,9 @@ register_wide_hw_breakpoint(struct perf_event_attr *attr,
 			    perf_overflow_handler_t triggered,
 			    void *context);
 
+int modify_local_hw_breakpoint_addr(struct perf_event *bp,
+				    unsigned long addr);
+
 extern int register_perf_hw_breakpoint(struct perf_event *bp);
 extern void unregister_hw_breakpoint(struct perf_event *bp);
 extern void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events);
@@ -124,6 +127,9 @@ register_wide_hw_breakpoint(struct perf_event_attr *attr,
 			    perf_overflow_handler_t triggered,
 			    void *context)		{ return NULL; }
 static inline int
+modify_local_hw_breakpoint_addr(struct perf_event *bp,
+				unsigned long addr) { return -EOPNOTSUPP; }
+static inline int
 register_perf_hw_breakpoint(struct perf_event *bp)	{ return -ENOSYS; }
 static inline void unregister_hw_breakpoint(struct perf_event *bp)	{ }
 static inline void
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 789add0c185a..0b1fc01f1934 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -888,6 +888,36 @@ void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 }
 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 
+/**
+ * modify_local_hw_breakpoint_addr - update a local breakpoint address
+ * @bp: the hwbp perf event for this CPU
+ * @addr: the new address for @bp
+ *
+ * Update only the address of an installed breakpoint on the local CPU without
+ * releasing and reserving its hardware slot. The caller must update other CPUs.
+ * Return 0, or -EOPNOTSUPP if the architecture does not support this operation.
+ */
+#ifdef CONFIG_HAVE_MODIFY_LOCAL_HW_BREAKPOINT_ADDR
+int modify_local_hw_breakpoint_addr(struct perf_event *bp,
+				    unsigned long addr)
+{
+	lockdep_assert_irqs_disabled();
+
+	counter_arch_bp(bp)->address = addr;
+	bp->attr.bp_addr = addr;
+	arch_modify_local_hw_breakpoint_addr(bp, addr);
+
+	return 0;
+}
+#else
+int modify_local_hw_breakpoint_addr(struct perf_event *bp,
+				    unsigned long addr)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+EXPORT_SYMBOL_GPL(modify_local_hw_breakpoint_addr);
+
 /**
  * hw_breakpoint_is_used - check if breakpoints are currently used
  *
-- 
2.53.0