Patch "perf/x86: Fix LBR related crashes on Intel Atom" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

perf/x86: Fix LBR related crashes on Intel Atom

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-x86-fix-lbr-related-crashes-on-intel-atom.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Stephane Eranian <[email protected]>
Date: Thu, 3 Dec 2015 23:33:17 +0100
Subject: perf/x86: Fix LBR related crashes on Intel Atom

From: Stephane Eranian <[email protected]>

commit 6fc2e83077b05a061afe9b24f2fdff7a0434eb67 upstream.

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.

---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -153,7 +153,7 @@ static void __intel_pmu_lbr_enable(bool
 	 */
 	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
 	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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/perf-x86-fix-lbr-related-crashes-on-intel-atom.patch