hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events

This patch rebase the implementation of the breakpoints API on top of
perf events instances.

Each breakpoints are now perf events that handle the
register scheduling, thread/cpu attachment, etc..

The new layering is now made as follows:

       ptrace       kgdb      ftrace   perf syscall
          \          |          /         /
           \         |         /         /
                                        /
            Core breakpoint API        /
                                      /
                     |               /
                     |              /

              Breakpoints perf events

                     |
                     |

               Breakpoints PMU ---- Debug Register constraints handling
                                    (Part of core breakpoint API)
                     |
                     |

             Hardware debug registers

Reasons of this rewrite:

- Use the centralized/optimized pmu registers scheduling,
  implying an easier arch integration
- More powerful register handling: perf attributes (pinned/flexible
  events, exclusive/non-exclusive, tunable period, etc...)

Impact:

- New perf ABI: the hardware breakpoints counters
- Ptrace breakpoints setting remains tricky and still needs some per
  thread breakpoints references.

Todo (in the order):

- Support breakpoints perf counter events for perf tools (ie: implement
  perf_bpcounter_event())
- Support from perf tools

Changes in v2:

- Follow the perf "event " rename
- The ptrace regression have been fixed (ptrace breakpoint perf events
  weren't released when a task ended)
- Drop the struct hw_breakpoint and store generic fields in
  perf_event_attr.
- Separate core and arch specific headers, drop
  asm-generic/hw_breakpoint.h and create linux/hw_breakpoint.h
- Use new generic len/type for breakpoint
- Handle off case: when breakpoints api is not supported by an arch

Changes in v3:

- Fix broken CONFIG_KVM, we need to propagate the breakpoint api
  changes to kvm when we exit the guest and restore the bp registers
  to the host.

Changes in v4:

- Drop the hw_breakpoint_restore() stub as it is only used by KVM
- EXPORT_SYMBOL_GPL hw_breakpoint_restore() as KVM can be built as a
  module
- Restore the breakpoints unconditionally on kvm guest exit:
  TIF_DEBUG_THREAD doesn't anymore cover every cases of running
  breakpoints and vcpu->arch.switch_db_regs might not always be
  set when the guest used debug registers.
  (Waiting for a reliable optimization)

Changes in v5:

- Split-up the asm-generic/hw-breakpoint.h moving to
  linux/hw_breakpoint.h into a separate patch
- Optimize the breakpoints restoring while switching from kvm guest
  to host. We only want to restore the state if we have active
  breakpoints to the host, otherwise we don't care about messed-up
  address registers.
- Add asm/hw_breakpoint.h to Kbuild
- Fix bad breakpoint type in trace_selftest.c

Changes in v6:

- Fix wrong header inclusion in trace.h (triggered a build
  error with CONFIG_FTRACE_SELFTEST

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jan Kiszka <jan.kiszka@web.de>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Paul Mundt <lethal@linux-sh.org>

1 files changed, 25 insertions, 1 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 8d54e6d25eeb..cead64ea6c15 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -18,6 +18,10 @@
 #include <linux/ioctl.h>
 #include <asm/byteorder.h>
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+#include <asm/hw_breakpoint.h>
+#endif
+
 /*
  * User-space ABI bits:
  */
@@ -31,6 +35,7 @@ enum perf_type_id {
         PERF_TYPE_TRACEPOINT                    = 2,
         PERF_TYPE_HW_CACHE                      = 3,
         PERF_TYPE_RAW                           = 4,
+        PERF_TYPE_BREAKPOINT                    = 5,
 
         PERF_TYPE_MAX,                          /* non-ABI */
 };
@@ -207,6 +212,15 @@ struct perf_event_attr {
                 __u32           wakeup_events;    /* wakeup every n events */
                 __u32           wakeup_watermark; /* bytes before wakeup   */
         };
+
+        union {
+                struct { /* Hardware breakpoint info */
+                        __u64           bp_addr;
+                        __u32           bp_type;
+                        __u32           bp_len;
+                };
+        };
+
         __u32                   __reserved_2;
 
         __u64                   __reserved_3;
@@ -476,6 +490,11 @@ struct hw_perf_event {
                         atomic64_t      count;
                         struct hrtimer  hrtimer;
                 };
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+                union { /* breakpoint */
+                        struct arch_hw_breakpoint       info;
+                };
+#endif
         };
         atomic64_t                      prev_count;
         u64                             sample_period;
@@ -588,7 +607,7 @@ struct perf_event {
         u64                             tstamp_running;
         u64                             tstamp_stopped;
 
-        struct perf_event_attr  attr;
+        struct perf_event_attr          attr;
         struct hw_perf_event            hw;
 
         struct perf_event_context       *ctx;
@@ -643,6 +662,8 @@ struct perf_event {
 
         perf_callback_t                 callback;
 
+        perf_callback_t                 event_callback;
+
 #endif /* CONFIG_PERF_EVENTS */
 };
 
@@ -831,6 +852,7 @@ extern int sysctl_perf_event_sample_rate;
 extern void perf_event_init(void);
 extern void perf_tp_event(int event_id, u64 addr, u64 count,
                                  void *record, int entry_size);
+extern void perf_bp_event(struct perf_event *event, void *data);
 
 #ifndef perf_misc_flags
 #define perf_misc_flags(regs)   (user_mode(regs) ? PERF_RECORD_MISC_USER : \
@@ -865,6 +887,8 @@ static inline int perf_event_task_enable(void)				{ return -EINVAL; }
 static inline void
 perf_sw_event(u32 event_id, u64 nr, int nmi,
                      struct pt_regs *regs, u64 addr)                    { }
+static inline void
+perf_bp_event(struct perf_event *event, void *data)             { }
 
 static inline void perf_event_mmap(struct vm_area_struct *vma)          { }
 static inline void perf_event_comm(struct task_struct *tsk)             { }