From 6c0aca288e726405b01dacb12cac556454d34b2a Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 11 Nov 2010 21:18:43 +0100 Subject: x86: Ignore trap bits on single step exceptions When a single step exception fires, the trap bits, used to signal hardware breakpoints, are in a random state. These trap bits might be set if another exception will follow, like a breakpoint in the next instruction, or a watchpoint in the previous one. Or there can be any junk there. So if we handle these trap bits during the single step exception, we are going to handle an exception twice, or we are going to handle junk. Just ignore them in this case. This fixes https://bugzilla.kernel.org/show_bug.cgi?id=21332 Reported-by: Michael Stefaniuc Signed-off-by: Frederic Weisbecker Cc: Rafael J. Wysocki Cc: Maciej Rutecki Cc: Alexandre Julliard Cc: Jason Wessel Cc: All since 2.6.33.x --- arch/x86/kernel/hw_breakpoint.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index ff15c9dcc25d..42c594254507 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -433,6 +433,10 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args) dr6_p = (unsigned long *)ERR_PTR(args->err); dr6 = *dr6_p; + /* If it's a single step, TRAP bits are random */ + if (dr6 & DR_STEP) + return NOTIFY_DONE; + /* Do an early return if no trap bits are set in DR6 */ if ((dr6 & DR_TRAP_BITS) == 0) return NOTIFY_DONE; -- cgit v1.2.3-55-g7522 From 3c502e7a0255d82621ff25d60cc816624830497e Mon Sep 17 00:00:00 2001 From: Jason Wessel Date: Thu, 4 Nov 2010 17:33:01 -0500 Subject: perf,hw_breakpoint: Initialize hardware api earlier When using early debugging, the kernel does not initialize the hw_breakpoint API early enough and causes the late initialization of the kernel debugger to fail. The boot arguments are: earlyprintk=vga ekgdboc=kbd kgdbwait Then simply type "go" at the kdb prompt and boot. The kernel will later emit the message: kgdb: Could not allocate hwbreakpoints And at that point the kernel debugger will cease to work correctly. The solution is to initialize the hw_breakpoint at the same time that all the other perf call backs are initialized instead of using a core_initcall() initialization which happens well after the kernel debugger can make use of hardware breakpoints. Signed-off-by: Jason Wessel CC: Frederic Weisbecker CC: Ingo Molnar CC: Peter Zijlstra LKML-Reference: <4CD3396D.1090308@windriver.com> Signed-off-by: Frederic Weisbecker --- include/linux/hw_breakpoint.h | 4 ++++ kernel/hw_breakpoint.c | 3 +-- kernel/perf_event.c | 6 ++++++ 3 files changed, 11 insertions(+), 2 deletions(-) diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h index a2d6ea49ec56..d1e55fed2c7d 100644 --- a/include/linux/hw_breakpoint.h +++ b/include/linux/hw_breakpoint.h @@ -33,6 +33,8 @@ enum bp_type_idx { #ifdef CONFIG_HAVE_HW_BREAKPOINT +extern int __init init_hw_breakpoint(void); + static inline void hw_breakpoint_init(struct perf_event_attr *attr) { memset(attr, 0, sizeof(*attr)); @@ -108,6 +110,8 @@ static inline struct arch_hw_breakpoint *counter_arch_bp(struct perf_event *bp) #else /* !CONFIG_HAVE_HW_BREAKPOINT */ +static inline int __init init_hw_breakpoint(void) { return 0; } + static inline struct perf_event * register_user_hw_breakpoint(struct perf_event_attr *attr, perf_overflow_handler_t triggered, diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c index 2c9120f0afca..e5325825aeb6 100644 --- a/kernel/hw_breakpoint.c +++ b/kernel/hw_breakpoint.c @@ -620,7 +620,7 @@ static struct pmu perf_breakpoint = { .read = hw_breakpoint_pmu_read, }; -static int __init init_hw_breakpoint(void) +int __init init_hw_breakpoint(void) { unsigned int **task_bp_pinned; int cpu, err_cpu; @@ -655,6 +655,5 @@ static int __init init_hw_breakpoint(void) return -ENOMEM; } -core_initcall(init_hw_breakpoint); diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 517d827f4982..05b7d8c72c6c 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -31,6 +31,7 @@ #include #include #include +#include #include @@ -6295,6 +6296,8 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) void __init perf_event_init(void) { + int ret; + perf_event_init_all_cpus(); init_srcu_struct(&pmus_srcu); perf_pmu_register(&perf_swevent); @@ -6302,4 +6305,7 @@ void __init perf_event_init(void) perf_pmu_register(&perf_task_clock); perf_tp_register(); perf_cpu_notifier(perf_cpu_notify); + + ret = init_hw_breakpoint(); + WARN(ret, "hw_breakpoint initialization failed with: %d", ret); } -- cgit v1.2.3-55-g7522