[PATCH] [LBR] Dump LBRs on Oops
From: Emmanuel Berthier
Date: Fri Nov 21 2014 - 12:04:55 EST
The purpose of this patch is to stop LBR at the early stage of
Exception Handling, and dump its content later in the dumpstack
process.
Only for X86_64 yet.
Signed-off-by: Emmanuel Berthier <emmanuel.berthier@xxxxxxxxx>
---
arch/x86/Kconfig.debug | 9 ++++++
arch/x86/include/asm/processor.h | 1 +
arch/x86/kernel/cpu/common.c | 4 +++
arch/x86/kernel/cpu/perf_event.h | 2 ++
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 12 +++++--
arch/x86/kernel/dumpstack_64.c | 47 ++++++++++++++++++++++++++--
arch/x86/kernel/entry_64.S | 40 +++++++++++++++++++++++
7 files changed, 111 insertions(+), 4 deletions(-)
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 61bd2ad..7a998b2 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -323,4 +323,13 @@ config X86_DEBUG_STATIC_CPU_HAS
If unsure, say N.
+config LBR_DUMP_ON_EXCEPTION
+ bool "Dump Last Branch Records on Oops"
+ depends on DEBUG_KERNEL && X86_64
+ ---help---
+ Enabling this option turns on LBR recording and dump during Oops.
+
+ This might help diagnose exceptions where faulting code
+ is not easy to determine from the call stack.
+
endmenu
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index eb71ec7..0c3ed67 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -462,6 +462,7 @@ DECLARE_PER_CPU(struct irq_stack *, softirq_stack);
extern unsigned int xstate_size;
extern void free_thread_xstate(struct task_struct *);
extern struct kmem_cache *task_xstate_cachep;
+extern unsigned int lbr_dump_on_exception;
struct perf_event;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4b4f78c..f49a26c 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1238,6 +1238,10 @@ DEFINE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);
#endif /* CONFIG_X86_64 */
+#ifdef CONFIG_LBR_DUMP_ON_EXCEPTION
+unsigned int lbr_dump_on_exception = 1;
+#endif
+
/*
* Clear all 6 debug registers:
*/
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index fc5eb39..ed9de7f 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -731,6 +731,8 @@ void intel_pmu_lbr_enable_all(void);
void intel_pmu_lbr_disable_all(void);
+void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc);
+
void intel_pmu_lbr_read(void);
void intel_pmu_lbr_init_core(void);
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 45fa730..baa840c 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -4,7 +4,9 @@
#include <asm/perf_event.h>
#include <asm/msr.h>
#include <asm/insn.h>
-
+#ifdef CONFIG_LBR_DUMP_ON_EXCEPTION
+#include <asm/processor.h>
+#endif
#include "perf_event.h"
enum {
@@ -135,6 +137,9 @@ static void __intel_pmu_lbr_enable(void)
u64 debugctl;
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ if (IS_ENABLED(CONFIG_LBR_DUMP_ON_EXCEPTION))
+ lbr_dump_on_exception = 0;
+
if (cpuc->lbr_sel)
wrmsrl(MSR_LBR_SELECT, cpuc->lbr_sel->config);
@@ -147,6 +152,9 @@ static void __intel_pmu_lbr_disable(void)
{
u64 debugctl;
+ if (IS_ENABLED(CONFIG_LBR_DUMP_ON_EXCEPTION))
+ lbr_dump_on_exception = 1;
+
rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
debugctl &= ~(DEBUGCTLMSR_LBR | DEBUGCTLMSR_FREEZE_LBRS_ON_PMI);
wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
@@ -278,7 +286,7 @@ static void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)
* is the same as the linear address, allowing us to merge the LIP and EIP
* LBR formats.
*/
-static void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
+void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
{
unsigned long mask = x86_pmu.lbr_nr - 1;
int lbr_format = x86_pmu.intel_cap.lbr_format;
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 1abcb50..fd78477 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -15,7 +15,10 @@
#include <linux/nmi.h>
#include <asm/stacktrace.h>
-
+#ifdef CONFIG_LBR_DUMP_ON_EXCEPTION
+#include <asm/processor.h>
+#include "cpu/perf_event.h"
+#endif
#define N_EXCEPTION_STACKS_END \
(N_EXCEPTION_STACKS + DEBUG_STKSZ/EXCEPTION_STKSZ - 2)
@@ -295,6 +298,41 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
show_trace_log_lvl(task, regs, sp, bp, log_lvl);
}
+void show_lbrs(void)
+{
+ if (IS_ENABLED(CONFIG_LBR_DUMP_ON_EXCEPTION)) {
+ u64 debugctl;
+ int i, lbr_on;
+
+ rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+ lbr_on = debugctl & DEBUGCTLMSR_LBR;
+
+ pr_info("Last Branch Records:");
+ if (!lbr_dump_on_exception) {
+ pr_cont(" (Disabled by perf_event)\n");
+ } else if (x86_pmu.lbr_nr == 0) {
+ pr_cont(" (x86_model unknown, check intel_pmu_init())\n");
+ } else if (lbr_on) {
+ pr_cont(" (not halted)\n");
+ } else {
+ struct cpu_hw_events *cpuc =
+ this_cpu_ptr(&cpu_hw_events);
+
+ intel_pmu_lbr_read_64(cpuc);
+
+ pr_cont("\n");
+ for (i = 0; i < cpuc->lbr_stack.nr; i++) {
+ pr_info(" to: [<%016llx>] ",
+ cpuc->lbr_entries[i].to);
+ print_symbol("%s\n", cpuc->lbr_entries[i].to);
+ pr_info(" from: [<%016llx>] ",
+ cpuc->lbr_entries[i].from);
+ print_symbol("%s\n", cpuc->lbr_entries[i].from);
+ }
+ }
+ }
+}
+
void show_regs(struct pt_regs *regs)
{
int i;
@@ -314,10 +352,15 @@ void show_regs(struct pt_regs *regs)
unsigned char c;
u8 *ip;
+ /*
+ * Called before show_stack_log_lvl() as it could trig
+ * page_fault and reenable LBR
+ */
+ show_lbrs();
+
printk(KERN_DEFAULT "Stack:\n");
show_stack_log_lvl(NULL, regs, (unsigned long *)sp,
0, KERN_DEFAULT);
-
printk(KERN_DEFAULT "Code: ");
ip = (u8 *)regs->ip - code_prologue;
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index df088bb..120e989 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1035,6 +1035,42 @@ apicinterrupt IRQ_WORK_VECTOR \
irq_work_interrupt smp_irq_work_interrupt
#endif
+.macro STOP_LBR
+#ifdef CONFIG_LBR_DUMP_ON_EXCEPTION
+ testl $1, lbr_dump_on_exception
+ jz 1f
+ push %rax
+ push %rcx
+ push %rdx
+ movl $MSR_IA32_DEBUGCTLMSR, %ecx
+ rdmsr
+ and $~1, %eax /* Disable LBR recording */
+ wrmsr
+ pop %rdx
+ pop %rcx
+ pop %rax
+1:
+#endif
+.endm
+
+.macro START_LBR
+#ifdef CONFIG_LBR_DUMP_ON_EXCEPTION
+ testl $1, lbr_dump_on_exception
+ jz 1f
+ push %rax
+ push %rcx
+ push %rdx
+ movl $MSR_IA32_DEBUGCTLMSR, %ecx
+ rdmsr
+ or $1, %eax /* Enable LBR recording */
+ wrmsr
+ pop %rdx
+ pop %rcx
+ pop %rax
+1:
+#endif
+.endm
+
/*
* Exception entry points.
*/
@@ -1063,6 +1099,8 @@ ENTRY(\sym)
subq $ORIG_RAX-R15, %rsp
CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
+ STOP_LBR
+
.if \paranoid
call save_paranoid
.else
@@ -1094,6 +1132,8 @@ ENTRY(\sym)
call \do_sym
+ START_LBR
+
.if \shift_ist != -1
addq $EXCEPTION_STKSZ, INIT_TSS_IST(\shift_ist)
.endif
--
1.7.9.5
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