xtensa: support hardware breakpoints/watchpoints

Use perf framework to manage hardware instruction and data breakpoints.
Add two new ptrace calls: PTRACE_GETHBPREGS and PTRACE_SETHBPREGS to
query and set instruction and data breakpoints.
Address bit 0 choose instruction (0) or data (1) break register, bits
31..1 are the register number.
Both calls transfer two 32-bit words: address (0) and control (1).
Instruction breakpoint contorl word is 0 to clear breakpoint, 1 to set.
Data breakpoint control word bit 31 is 'trigger on store', bit 30 is
'trigger on load, bits 29..0 are length. Length 0 is used to clear a
breakpoint. To set a breakpoint length must be a power of 2 in the range
1..64 and the address must be length-aligned.

Introduce new thread_info flag: TIF_DB_DISABLED. Set it if debug
exception is raised by the kernel code accessing watched userspace
address and disable corresponding data breakpoint. On exit to userspace
check that flag and, if set, restore all data breakpoints.

Handle debug exceptions raised with PS.EXCM set. This may happen when
window overflow/underflow handler or fast exception handler hits data
breakpoint, in which case save and disable all data breakpoints,
single-step faulting instruction and restore data breakpoints.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

7 files changed, 77 insertions, 5 deletions

diff --git a/arch/xtensa/include/asm/hw_breakpoint.h b/arch/xtensa/include/asm/hw_breakpoint.h
new file mode 100644
index 000000000000..dbe3053b284a
--- /dev/null
+++ b/arch/xtensa/include/asm/hw_breakpoint.h
@@ -0,0 +1,58 @@
+/*
+ * Xtensa hardware breakpoints/watchpoints handling functions
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2016 Cadence Design Systems Inc.
+ */
+
+#ifndef __ASM_XTENSA_HW_BREAKPOINT_H
+#define __ASM_XTENSA_HW_BREAKPOINT_H
+
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+
+#include <linux/kdebug.h>
+#include <linux/types.h>
+#include <uapi/linux/hw_breakpoint.h>
+
+/* Breakpoint */
+#define XTENSA_BREAKPOINT_EXECUTE	0
+
+/* Watchpoints */
+#define XTENSA_BREAKPOINT_LOAD		1
+#define XTENSA_BREAKPOINT_STORE		2
+
+struct arch_hw_breakpoint {
+	unsigned long address;
+	u16 len;
+	u16 type;
+};
+
+struct perf_event;
+struct pt_regs;
+struct task_struct;
+
+int hw_breakpoint_slots(int type);
+int arch_check_bp_in_kernelspace(struct perf_event *bp);
+int arch_validate_hwbkpt_settings(struct perf_event *bp);
+int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+				    unsigned long val, void *data);
+
+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 check_hw_breakpoint(struct pt_regs *regs);
+void clear_ptrace_hw_breakpoint(struct task_struct *tsk);
+
+#else
+
+struct task_struct;
+
+static inline void clear_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+}
+
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+#endif /* __ASM_XTENSA_HW_BREAKPOINT_H */
diff --git a/arch/xtensa/include/asm/irqflags.h b/arch/xtensa/include/asm/irqflags.h
index 8e090c709046..407606e576f8 100644
--- a/arch/xtensa/include/asm/irqflags.h
+++ b/arch/xtensa/include/asm/irqflags.h
@@ -13,6 +13,7 @@
 #define _XTENSA_IRQFLAGS_H
 
 #include <linux/types.h>
+#include <asm/processor.h>
 
 static inline unsigned long arch_local_save_flags(void)
 {
diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h
index 744ecf0dc3a4..d2e40d39c615 100644
--- a/arch/xtensa/include/asm/processor.h
+++ b/arch/xtensa/include/asm/processor.h
@@ -130,11 +130,10 @@ struct thread_struct {
 	unsigned long bad_vaddr; /* last user fault */
 	unsigned long bad_uaddr; /* last kernel fault accessing user space */
 	unsigned long error_code;
-
-	unsigned long ibreak[XCHAL_NUM_IBREAK];
-	unsigned long dbreaka[XCHAL_NUM_DBREAK];
-	unsigned long dbreakc[XCHAL_NUM_DBREAK];
-
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	struct perf_event *ptrace_bp[XCHAL_NUM_IBREAK];
+	struct perf_event *ptrace_wp[XCHAL_NUM_DBREAK];
+#endif
 	/* Make structure 16 bytes aligned. */
 	int align[0] __attribute__ ((aligned(16)));
 };
diff --git a/arch/xtensa/include/asm/regs.h b/arch/xtensa/include/asm/regs.h
index 4ba9f516b0e2..881a1134a4b4 100644
--- a/arch/xtensa/include/asm/regs.h
+++ b/arch/xtensa/include/asm/regs.h
@@ -28,6 +28,7 @@
 /*  Special registers.  */
 
 #define SREG_MR			32
+#define SREG_IBREAKENABLE	96
 #define SREG_IBREAKA		128
 #define SREG_DBREAKA		144
 #define SREG_DBREAKC		160
@@ -103,6 +104,8 @@
 
 /*  DEBUGCAUSE register fields.  */
 
+#define DEBUGCAUSE_DBNUM_MASK		0xf00
+#define DEBUGCAUSE_DBNUM_SHIFT		8	/* First bit of DBNUM field */
 #define DEBUGCAUSE_DEBUGINT_BIT		5	/* External debug interrupt */
 #define DEBUGCAUSE_BREAKN_BIT		4	/* BREAK.N instruction */
 #define DEBUGCAUSE_BREAK_BIT		3	/* BREAK instruction */
diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
index 9ad12c617184..7be2400f745a 100644
--- a/arch/xtensa/include/asm/thread_info.h
+++ b/arch/xtensa/include/asm/thread_info.h
@@ -111,6 +111,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_MEMDIE		5	/* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
 #define TIF_NOTIFY_RESUME	7	/* callback before returning to user */
+#define TIF_DB_DISABLED		8	/* debug trap disabled for syscall */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
diff --git a/arch/xtensa/include/asm/traps.h b/arch/xtensa/include/asm/traps.h
index 3ad151aee6af..2e69aa4b843f 100644
--- a/arch/xtensa/include/asm/traps.h
+++ b/arch/xtensa/include/asm/traps.h
@@ -70,6 +70,14 @@ struct debug_table {
 	void (*debug_exception)(void);
 	/* Temporary register save area */
 	unsigned long debug_save[1];
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	/* Save area for DBREAKC registers */
+	unsigned long dbreakc_save[XCHAL_NUM_DBREAK];
+	/* Saved ICOUNT register */
+	unsigned long icount_save;
+	/* Saved ICOUNTLEVEL register */
+	unsigned long icount_level_save;
+#endif
 };
 
 void debug_exception(void);
diff --git a/arch/xtensa/include/uapi/asm/ptrace.h b/arch/xtensa/include/uapi/asm/ptrace.h
index ee17aa842fdf..6ccbd9e38e35 100644
--- a/arch/xtensa/include/uapi/asm/ptrace.h
+++ b/arch/xtensa/include/uapi/asm/ptrace.h
@@ -72,6 +72,8 @@
 #define PTRACE_SETREGS		13
 #define PTRACE_GETXTREGS	18
 #define PTRACE_SETXTREGS	19
+#define PTRACE_GETHBPREGS	20
+#define PTRACE_SETHBPREGS	21
 
 
 #endif /* _UAPI_XTENSA_PTRACE_H */