linux-kernel - [tip:perf/core] perf/x86/intel/pt: Untangle pt_buffer_reset

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <tip-f73ec48c90016f89d05726f6c48e66991a790fd7@git.kernel.org>
Date:	Wed, 27 May 2015 03:02:21 -0700
From:	tip-bot for Alexander Shishkin <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, alexander.shishkin@...ux.intel.com,
	peterz@...radead.org, paulus@...ba.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	hpa@...or.com, mingo@...nel.org
Subject: [tip:perf/core] perf/x86/intel/pt:
  Untangle pt_buffer_reset_markers()

Commit-ID:  f73ec48c90016f89d05726f6c48e66991a790fd7
Gitweb:     http://git.kernel.org/tip/f73ec48c90016f89d05726f6c48e66991a790fd7
Author:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
AuthorDate: Fri, 22 May 2015 18:30:22 +0300
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 27 May 2015 09:16:20 +0200

perf/x86/intel/pt: Untangle pt_buffer_reset_markers()

Currently, pt_buffer_reset_markers() is a difficult to read knot of
arithmetics with a redundant check for multiple-entry TOPA capability,
a commented out wakeup marker placement and a logical error wrt to
stop marker placement. The latter happens when write head is not page
aligned and results in stop marker being placed one page earlier than
it actually should.

All these problems only affect PT implementations that support
multiple-entry TOPA tables (read: proper scatter-gather).

For single-entry TOPA implementations, there is no functional impact.

This patch deals with all of the above. Tested on both single-entry
and multiple-entry TOPA PT implementations.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: acme@...radead.org
Cc: adrian.hunter@...el.com
Cc: hpa@...or.com
Link: http://lkml.kernel.org/r/1432308626-18845-4-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/perf_event_intel_pt.c | 34 ++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index ffe666c..5b804f9 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -615,7 +615,8 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 				   struct perf_output_handle *handle)
 
 {
-	unsigned long idx, npages, end;
+	unsigned long head = local64_read(&buf->head);
+	unsigned long idx, npages, wakeup;
 
 	if (buf->snapshot)
 		return 0;
@@ -634,17 +635,26 @@ static int pt_buffer_reset_markers(struct pt_buffer *buf,
 	buf->topa_index[buf->stop_pos]->stop = 0;
 	buf->topa_index[buf->intr_pos]->intr = 0;
 
-	if (pt_cap_get(PT_CAP_topa_multiple_entries)) {
-		npages = (handle->size + 1) >> PAGE_SHIFT;
-		end = (local64_read(&buf->head) >> PAGE_SHIFT) + npages;
-		/*if (end > handle->wakeup >> PAGE_SHIFT)
-		  end = handle->wakeup >> PAGE_SHIFT;*/
-		idx = end & (buf->nr_pages - 1);
-		buf->stop_pos = idx;
-		idx = (local64_read(&buf->head) >> PAGE_SHIFT) + npages - 1;
-		idx &= buf->nr_pages - 1;
-		buf->intr_pos = idx;
-	}
+	/* how many pages till the STOP marker */
+	npages = handle->size >> PAGE_SHIFT;
+
+	/* if it's on a page boundary, fill up one more page */
+	if (!offset_in_page(head + handle->size + 1))
+		npages++;
+
+	idx = (head >> PAGE_SHIFT) + npages;
+	idx &= buf->nr_pages - 1;
+	buf->stop_pos = idx;
+
+	wakeup = handle->wakeup >> PAGE_SHIFT;
+
+	/* in the worst case, wake up the consumer one page before hard stop */
+	idx = (head >> PAGE_SHIFT) + npages - 1;
+	if (idx > wakeup)
+		idx = wakeup;
+
+	idx &= buf->nr_pages - 1;
+	buf->intr_pos = idx;
 
 	buf->topa_index[buf->stop_pos]->stop = 1;
 	buf->topa_index[buf->intr_pos]->intr = 1;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/