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>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index e2fad0cdca2fe9c88f560e2dc25e3d40e823c3a2..1390148ee2e67ab6411bd9a6af00e30151686bbc 100644 (file)
--- 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;