• Frederic Weisbecker's avatar
    hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events · 24f1e32c
    Frederic Weisbecker authored
    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: default avatarFrederic 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>
    24f1e32c
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