[RFC PATCH 3/6] HWBP: Add modify_wide_hw_breakpoint_local() API

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add modify_wide_hw_breakpoint_local() arch-wide interface which allows
hwbp users to update watch address on-line. This is available if the
arch supports CONFIG_HAVE_REINSTALL_HW_BREAKPOINT.
Note that this can not change the type because it does not release and
reserve the hwbp slot based on type.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 arch/Kconfig                         |   10 +++++++++
 arch/x86/Kconfig                     |    1 +
 arch/x86/include/asm/hw_breakpoint.h |    2 ++
 arch/x86/kernel/hw_breakpoint.c      |   11 ++++++++++
 include/linux/hw_breakpoint.h        |    6 ++++++
 kernel/events/hw_breakpoint.c        |   36 ++++++++++++++++++++++++++++++++++
 6 files changed, 66 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index d1b4ffd6e085..e4787fc814df 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -418,6 +418,16 @@ config HAVE_MIXED_BREAKPOINTS_REGS
 	  Select this option if your arch implements breakpoints under the
 	  latter fashion.
 
+config HAVE_REINSTALL_HW_BREAKPOINT
+	bool
+	depends on HAVE_HW_BREAKPOINT
+	help
+	  Depending on the arch implementation of hardware breakpoints,
+	  some of them are able to update the breakpoint configuration
+	  without release and reserve the hardware breakpoint register.
+	  What configuration is able to update depends on hardware and
+	  software implementation.
+
 config HAVE_USER_RETURN_NOTIFIER
 	bool
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 58d890fe2100..49d4ce2af94c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -247,6 +247,7 @@ config X86
 	select HAVE_FUNCTION_TRACER
 	select HAVE_GCC_PLUGINS
 	select HAVE_HW_BREAKPOINT
+	select HAVE_REINSTALL_HW_BREAKPOINT
 	select HAVE_IOREMAP_PROT
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK	if X86_64
 	select HAVE_IRQ_TIME_ACCOUNTING
diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h
index bb7c70ad22fe..b3db25eb613f 100644
--- a/arch/x86/include/asm/hw_breakpoint.h
+++ b/arch/x86/include/asm/hw_breakpoint.h
@@ -64,6 +64,8 @@ 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);
 
+bool hw_breakpoint_arch_same_type(struct arch_hw_breakpoint *hw,
+				  struct perf_event_attr *attr);
 extern void
 arch_fill_perf_breakpoint(struct perf_event *bp);
 
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 89135229ed21..7dfc88ff6cd9 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -278,6 +278,17 @@ int arch_bp_generic_fields(int x86_len, int x86_type,
 	return 0;
 }
 
+bool hw_breakpoint_arch_same_type(struct arch_hw_breakpoint *hw,
+				  struct perf_event_attr *attr)
+{
+	int glen, gtype;
+
+	if (arch_bp_generic_fields(hw->len, hw->type, &glen, &gtype) < 0)
+		return false;
+
+	return gtype == attr->bp_type;
+}
+
 /*
  * Check for virtual address in kernel space.
  */
diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index db199d653dd1..ea373f2587f8 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);
 
+extern int modify_wide_hw_breakpoint_local(struct perf_event *bp,
+					   struct perf_event_attr *attr);
+
 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_wide_hw_breakpoint_local(struct perf_event *bp,
+				struct perf_event_attr *attr) { return -ENOSYS; }
+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 8ec2cb688903..473a5b76941d 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -887,6 +887,42 @@ void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 }
 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 
+/**
+ * modify_wide_hw_breakpoint_local - update breakpoint config for local cpu
+ * @bp: the hwbp perf event for this cpu
+ * @attr: the new attribute for @bp
+ *
+ * This does not release and reserve the slot of HWBP, just reuse the current
+ * slot on local CPU. So the users must update the other CPUs by themselves.
+ * Also, since this does not release/reserve the slot, this can not change the
+ * type of the HWBP.
+ * Return err if attr is invalid or the cpu fails to update debug register
+ * for new @attr.
+ */
+#ifdef CONFIG_HAVE_REINSTALL_HW_BREAKPOINT
+int modify_wide_hw_breakpoint_local(struct perf_event *bp,
+				    struct perf_event_attr *attr)
+{
+	int ret;
+
+	if (!hw_breakpoint_arch_same_type(counter_arch_bp(bp), attr))
+		return -EINVAL;
+
+	ret = hw_breakpoint_arch_parse(bp, attr, counter_arch_bp(bp));
+	if (ret)
+		return ret;
+
+	return arch_reinstall_hw_breakpoint(bp);
+}
+#else
+int modify_wide_hw_breakpoint_local(struct perf_event *bp,
+				    struct perf_event_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+EXPORT_SYMBOL_GPL(modify_wide_hw_breakpoint_local);
+
 /**
  * hw_breakpoint_is_used - check if breakpoints are currently used
  *