On Thu, May 27, 2010 at 04:19:40PM +1000, Paul Mackerras wrote: > On Tue, May 25, 2010 at 02:44:20PM +0530, K.Prasad wrote: > > > Implement perf-events based hw-breakpoint interfaces for PowerPC Book III S > > processors. These interfaces help arbitrate requests from various users and > > schedules them as appropriate. > > A few comments on the code below... >
I've posted a new patchset that addresses almost all of your comments. Please find them here: linuxppc-dev message-id: 20100528063924.ga8...@in.ibm.com > > +int __kprobes hw_breakpoint_handler(struct die_args *args) > > +{ > > + bool is_ptrace_bp = false; > > + int rc = NOTIFY_STOP; > > + struct perf_event *bp; > > + struct pt_regs *regs = args->regs; > > + unsigned long dar = regs->dar; > > + int stepped = 1; > > + struct arch_hw_breakpoint *info; > > + > > + /* Disable breakpoints during exception handling */ > > + set_dabr(0); > > + /* > > + * The counter may be concurrently released but that can only > > + * occur from a call_rcu() path. We can then safely fetch > > + * the breakpoint, use its callback, touch its counter > > + * while we are in an rcu_read_lock() path. > > + */ > > + rcu_read_lock(); > > + > > + bp = __get_cpu_var(bp_per_reg); > > + if (!bp) > > + goto out; > > + info = counter_arch_bp(bp); > > + is_ptrace_bp = (bp->overflow_handler == ptrace_triggered) ? > > + true : false; > > + > > + /* > > + * Verify if dar lies within the address range occupied by the symbol > > + * being watched to filter extraneous exceptions. > > + */ > > + if (!((bp->attr.bp_addr <= dar) && > > + (dar <= (bp->attr.bp_addr + bp->attr.bp_len))) && > > + (!is_ptrace_bp)) > > + /* > > + * This exception is triggered not because of a memory access on > > + * the monitored variable but in the double-word address range > > + * in which it is contained. We will consume this exception, > > + * considering it as 'noise'. > > + */ > > + goto restore_bp; > > At this point we have to do the single-stepping, because the NIP is > still pointing at the instruction that caused the exception, and if we > just return to it with DABR set we won't make any progress, we'll just > take the same exception again immediately. > I don't know how I convinced myself earlier that this would work :-) Given that the instructions needs to be emulated in the same manner as others, I've re-used the ptrace_bps[] member in 'thread_struct' as a flag to indicate such breakpoints. This will be later checked in single_step_dabr_instruction() to prevent invocation of perf_event_bp(). > > +/* > > + * Handle single-step exceptions following a DABR hit. > > + */ > > +int __kprobes single_step_dabr_instruction(struct die_args *args) > > +{ > > + struct pt_regs *regs = args->regs; > > + struct perf_event *bp = NULL; > > + struct arch_hw_breakpoint *bp_info; > > + > > + bp = current->thread.last_hit_ubp; > > + /* > > + * Check if we are single-stepping as a result of a > > + * previous HW Breakpoint exception > > + */ > > + if (!bp) > > + return NOTIFY_DONE; > > + > > + bp_info = counter_arch_bp(bp); > > + > > + /* > > + * We shall invoke the user-defined callback function in the single > > + * stepping handler to confirm to 'trigger-after-execute' semantics > > + */ > > + perf_bp_event(bp, regs); > > + > > + /* > > + * Do not disable MSR_SE if the process was already in > > + * single-stepping mode. > > + */ > > + if (!test_thread_flag(TIF_SINGLESTEP)) > > + regs->msr &= ~MSR_SE; > > + > > + set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION); > > + return NOTIFY_STOP; > > +} > > Nowhere in here do we reset current->thread.last_hit_ubp, yet other > parts of the code assume that .last_hit_ubp != NULL means that we are > currently single-stepping. I think we need to clear .last_hit_ubp > here. > True, made the change. > > Index: linux-2.6.ppc64_test/arch/powerpc/kernel/process.c > > =================================================================== > > --- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/process.c > > +++ linux-2.6.ppc64_test/arch/powerpc/kernel/process.c > > @@ -462,8 +462,14 @@ struct task_struct *__switch_to(struct t > > #ifdef CONFIG_PPC_ADV_DEBUG_REGS > > switch_booke_debug_regs(&new->thread); > > #else > > +/* > > + * For PPC_BOOK3S_64, we use the hw-breakpoint interfaces that would > > + * schedule DABR > > + */ > > +#ifndef CONFIG_HAVE_HW_BREAKPOINT > > if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr)) > > set_dabr(new->thread.dabr); > > +#endif /* CONFIG_HAVE_HW_BREAKPOINT */ > > #endif > > Have you checked all the places that set_dabr is called to see whether > they are still needed with CONFIG_HAVE_HW_BREAKPOINT? > Yes. All invocations of set_dabr() or their caller functions are enclosed within #ifdef CONFIG_HAVE_HW_BREAKPOINT. > > Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/cputable.h > > =================================================================== > > --- linux-2.6.ppc64_test.orig/arch/powerpc/include/asm/cputable.h > > +++ linux-2.6.ppc64_test/arch/powerpc/include/asm/cputable.h > > @@ -516,6 +516,10 @@ static inline int cpu_has_feature(unsign > > & feature); > > } > > > > +#ifdef CONFIG_HAVE_HW_BREAKPOINT > > +#define HBP_NUM 1 > > +#endif /* CONFIG_HAVE_HW_BREAKPOINT */ > > Why is this defined here, not in <asm/hw_breakpoint.h> ? > We need HBP_NUM value for arch/powerpc/include/asm/processor.h and if asm/hw_breakpoint.h is included there, it caused recursive dependancies. After more discussions with the community (as in linuxppc-dev: message-id: 20100330101234.ga14...@in.ibm.com) we finally decided to put it in cputable.h We will have more related definitions to accompany this when support for BookIII E is brought in. Thanks, K.Prasad _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev