[4.2.y-ckt stable] Patch "perf/x86/intel/pt: Generate PMI in the STOP region as well" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    perf/x86/intel/pt: Generate PMI in the STOP region as well

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From 36052113b27a25685c936a8360b4917a775943d2 Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin at linux.intel.com>
Date: Tue, 10 May 2016 16:18:32 +0300
Subject: perf/x86/intel/pt: Generate PMI in the STOP region as well

commit ab92b232ae05c382c3df0e3d6a5c6d16b639ac8c upstream.

Currently, the PT driver always sets the PMI bit one region (page) before
the STOP region so that we can wake up the consumer before we run out of
room in the buffer and have to disable the event. However, we also need
an interrupt in the last output region, so that we actually get to disable
the event (if no more room from new data is available at that point),
otherwise hardware just quietly refuses to start, but the event is
scheduled in and we end up losing trace data till the event gets removed.

For a cpu-wide event it is even worse since there may not be any
re-scheduling at all and no chance for the ring buffer code to notice
that its buffer is filled up and the event needs to be disabled (so that
the consumer can re-enable it when it finishes reading the data out). In
other words, all the trace data will be lost after the buffer gets filled
up.

This patch makes PT also generate a PMI when the last output region is
full.

Reported-by: Markus Metzger <markus.t.metzger at intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin at linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Cc: Arnaldo Carvalho de Melo <acme at infradead.org>
Cc: Arnaldo Carvalho de Melo <acme at redhat.com>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Jiri Olsa <jolsa at redhat.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Stephane Eranian <eranian at google.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Vince Weaver <vincent.weaver at maine.edu>
Cc: vince at deater.net
Link: http://lkml.kernel.org/r/1462886313-13660-2-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
[ kamal: backport to 4.2-stable: file moved ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/cpu/perf_event_intel_pt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index 183de71..db9a245 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -626,6 +626,7 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,

 	/* clear STOP and INT from current entry */
 	buf->topa_index[buf->stop_pos]->stop = 0;
+	buf->topa_index[buf->stop_pos]->intr = 0;
 	buf->topa_index[buf->intr_pos]->intr = 0;

 	/* how many pages till the STOP marker */
@@ -650,6 +651,7 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 	buf->intr_pos = idx;

 	buf->topa_index[buf->stop_pos]->stop = 1;
+	buf->topa_index[buf->stop_pos]->intr = 1;
 	buf->topa_index[buf->intr_pos]->intr = 1;

 	return 0;
--
2.7.4