Patch "perf/x86: Fix full width counter, counter overflow" has been added to the 4.8-stable tree

[<gregkh@linuxfoundation.org>]

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

    perf/x86: Fix full width counter, counter overflow

to the 4.8-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-full-width-counter-counter-overflow.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 7f612a7f0bc13a2361a152862435b7941156b6af Mon Sep 17 00:00:00 2001
From: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Date: Tue, 29 Nov 2016 20:33:28 +0000
Subject: perf/x86: Fix full width counter, counter overflow

From: Peter Zijlstra (Intel) <peterz@infradead.org>

commit 7f612a7f0bc13a2361a152862435b7941156b6af upstream.

Lukasz reported that perf stat counters overflow handling is broken on KNL/SLM.

Both these parts have full_width_write set, and that does indeed have
a problem. In order to deal with counter wrap, we must sample the
counter at at least half the counter period (see also the sampling
theorem) such that we can unambiguously reconstruct the count.

However commit:

  069e0c3c4058 ("perf/x86/intel: Support full width counting")

sets the sampling interval to the full period, not half.

Fixing that exposes another issue, in that we must not sign extend the
delta value when we shift it right; the counter cannot have
decremented after all.

With both these issues fixed, counter overflow functions correctly
again.

Reported-by: Lukasz Odzioba <lukasz.odzioba@intel.com>
Tested-by: Liang, Kan <kan.liang@intel.com>
Tested-by: Odzioba, Lukasz <lukasz.odzioba@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
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: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 069e0c3c4058 ("perf/x86/intel: Support full width counting")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/events/core.c       |    2 +-
 arch/x86/events/intel/core.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -68,7 +68,7 @@ u64 x86_perf_event_update(struct perf_ev
 	int shift = 64 - x86_pmu.cntval_bits;
 	u64 prev_raw_count, new_raw_count;
 	int idx = hwc->idx;
-	s64 delta;
+	u64 delta;
 
 	if (idx == INTEL_PMC_IDX_FIXED_BTS)
 		return 0;
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4024,7 +4024,7 @@ __init int intel_pmu_init(void)
 
 	/* Support full width counters using alternative MSR range */
 	if (x86_pmu.intel_cap.full_width_write) {
-		x86_pmu.max_period = x86_pmu.cntval_mask;
+		x86_pmu.max_period = x86_pmu.cntval_mask >> 1;
 		x86_pmu.perfctr = MSR_IA32_PMC0;
 		pr_cont("full-width counters, ");
 	}


Patches currently in stable-queue which might be from peterz@infradead.org are

queue-4.8/sched-autogroup-fix-64-bit-kernel-nice-level-adjustment.patch
queue-4.8/locking-rtmutex-prevent-dequeue-vs.-unlock-race.patch
queue-4.8/perf-x86-fix-full-width-counter-counter-overflow.patch
queue-4.8/locking-rtmutex-use-read_once-in-rt_mutex_owner.patch