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.
Fixes: 96f3eda6 ("perf/x86/intel: Fix static checker warning in lbr enable")
Signed-off-by: Stephane Eranian <eran...@google.com>
---
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 11 +++++++----
1 file 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 e2fad0c..1390148 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;
--
1.9.1
--
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