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Commit 6fc2e830 authored by Stephane Eranian's avatar Stephane Eranian Committed by Ingo Molnar
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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: default avatarStephane Eranian <eranian@google.com>
Signed-off-by: default avatarPeter 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: 96f3eda6 ("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: default avatarIngo Molnar <mingo@kernel.org>
parent 61b87cae

arch/x86/kernel/cpu/perf_event_intel_lbr.c

+7 −4
Original line number Diff line number Diff line
@@ -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) {

		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;