perf/x86: Fix LBR related crashes on Intel Atom

This patches fixes the LBR kernel crashes on Intel Atom.

The kernel was assuming that if the CPU supports 64-bit format
LBR, then it has an LBR_SELECT MSR. Atom uses 64-bit LBR format
but does not have LBR_SELECT. That was causing NULL pointer
dereferences in a couple of places.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: kan.liang@intel.com
Fixes: 96f3eda67fcf ("perf/x86/intel: Fix static checker warning in lbr enable")
Link: http://lkml.kernel.org/r/1449182000-31524-2-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index e2fad0cdca2f..1390148ee2e6 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -161,7 +161,7 @@ static void __intel_pmu_lbr_enable(bool pmi)
          */
         if (cpuc->lbr_sel)
                 lbr_select = cpuc->lbr_sel->config & x86_pmu.lbr_sel_mask;
-        if (!pmi)
+        if (!pmi && cpuc->lbr_sel)
                 wrmsrl(MSR_LBR_SELECT, lbr_select);
 
         rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
@@ -430,7 +430,7 @@ static void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)
  */
 static void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
 {
-        bool need_info = !(cpuc->lbr_sel->config & LBR_NO_INFO);
+        bool need_info = false;
         unsigned long mask = x86_pmu.lbr_nr - 1;
         int lbr_format = x86_pmu.intel_cap.lbr_format;
         u64 tos = intel_pmu_lbr_tos();
@@ -438,8 +438,11 @@ static void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)
         int out = 0;
         int num = x86_pmu.lbr_nr;
 
-        if (cpuc->lbr_sel->config & LBR_CALL_STACK)
-                num = tos;
+        if (cpuc->lbr_sel) {
+                need_info = !(cpuc->lbr_sel->config & LBR_NO_INFO);
+                if (cpuc->lbr_sel->config & LBR_CALL_STACK)
+                        num = tos;
+        }
 
         for (i = 0; i < num; i++) {
                 unsigned long lbr_idx = (tos - i) & mask;