This backported patch should be applied to kernel 4.4. Otherwise
GPF/NULL pointer
derefer will happens on related platforms upon attempt to use perf in
some use cases
(perf record).
On 08/21/2017 06:57 PM, Denys Zagorui wrote:
From: Stephane Eranian <eranian@xxxxxxxxxx>
commit 6fc2e83077b05a061afe9b24f2fdff7a0434eb67 upstream.
This patches fixes the LBR kernel crashes on Intel Atom and Intel Xeon.
The kernel was assuming that if the CPU supports 64-bit format
LBR, then it has an LBR_SELECT MSR. Atom, Xeon uses 64-bit LBR
format but does not have LBR_SELECT. That was causing NULL
pointer dereferences in a couple of places.
Change-Id: Ia2a8290d9ad9553ea54fef81be7e9f8af4fbf9fa
Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: kan.liang@xxxxxxxxx
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@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Denys Zagorui <dzagorui@xxxxxxxxx>
---
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 8900400..2cdae69 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -153,7 +153,7 @@ static void __intel_pmu_lbr_enable(bool pmi)
*/
if (cpuc->lbr_sel)
lbr_select = cpuc->lbr_sel->config;
- if (!pmi)
+ if (!pmi && cpuc->lbr_sel)
wrmsrl(MSR_LBR_SELECT, lbr_select);
rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
@@ -432,8 +432,10 @@ 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) {
+ if (cpuc->lbr_sel->config & LBR_CALL_STACK)
+ num = tos;
+ }
for (i = 0; i < num; i++) {
unsigned long lbr_idx = (tos - i) & mask;