[PATCH v4 11/15] KVM: arm: add a function to keep track of host use of the debug registers

[Zhichao Huang <zhichao.huang@linaro.org>]

As we're about to implement a lazy world switch for debug registers,
we add a function reading the break/watch control variables directly to
indicate whether the host has enabled any break/watch points or not.

Signed-off-by: Zhichao Huang <zhichao.huang@linaro.org>
---
 arch/arm/include/asm/hw_breakpoint.h |  5 +++++
 arch/arm/kernel/hw_breakpoint.c      | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
index f2f4c61..6f375c5 100644
--- a/arch/arm/include/asm/hw_breakpoint.h
+++ b/arch/arm/include/asm/hw_breakpoint.h
@@ -66,9 +66,14 @@ int arch_install_hw_breakpoint(struct perf_event *bp);
 void arch_uninstall_hw_breakpoint(struct perf_event *bp);
 void hw_breakpoint_pmu_read(struct perf_event *bp);
 int hw_breakpoint_slots(int type);
+bool hw_breakpoint_enabled(void);
 
 #else
 static inline void clear_ptrace_hw_breakpoint(struct task_struct *tsk) {}
+static inline bool hw_breakpoint_enabled(void)
+{
+	return false;
+}
 
 #endif	/* CONFIG_HAVE_HW_BREAKPOINT */
 #endif  /* __ASSEMBLY */
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index dc7d0a9..f56788f 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -227,6 +227,27 @@ static int get_num_brps(void)
 	return core_has_mismatch_brps() ? brps - 1 : brps;
 }
 
+/* Indicate whether the host has enabled any break/watch points or not. */
+bool hw_breakpoint_enabled(void)
+{
+	struct perf_event **slots;
+	int i;
+
+	slots = this_cpu_ptr(bp_on_reg);
+	for (i = 0; i < core_num_brps; i++) {
+		if (slots[i])
+			return true;
+	}
+
+	slots = this_cpu_ptr(wp_on_reg);
+	for (i = 0; i < core_num_wrps; i++) {
+		if (slots[i])
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * In order to access the breakpoint/watchpoint control registers,
  * we must be running in debug monitor mode. Unfortunately, we can
-- 
1.7.12.4