linux-kernel - [tip:perf/core] bitmap.h, perf/core: Fix the mask in perf_output_sample

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Message-ID: <tip-29dd3288705f26cc27663e79061209dabce2d5b9@git.kernel.org>
Date:	Thu, 18 Aug 2016 03:53:01 -0700
From:	tip-bot for Madhavan Srinivasan <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	peterz@...radead.org, vincent.weaver@...ne.edu, mingo@...nel.org,
	eranian@...gle.com, acme@...hat.com, torvalds@...ux-foundation.org,
	jolsa@...nel.org, ynorov@...iumnetworks.com, acme@...nel.org,
	jolsa@...hat.com, alexander.shishkin@...ux.intel.com,
	hpa@...or.com, mpe@...erman.id.au, maddy@...ux.vnet.ibm.com
Subject: [tip:perf/core] bitmap.h, perf/core: Fix the mask in
 perf_output_sample_regs()

Commit-ID:  29dd3288705f26cc27663e79061209dabce2d5b9
Gitweb:     http://git.kernel.org/tip/29dd3288705f26cc27663e79061209dabce2d5b9
Author:     Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
AuthorDate: Wed, 17 Aug 2016 15:06:08 +0530
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 18 Aug 2016 10:44:20 +0200

bitmap.h, perf/core: Fix the mask in perf_output_sample_regs()

When decoding the perf_regs mask in perf_output_sample_regs(),
we loop through the mask using find_first_bit and find_next_bit functions.

While the exisiting code works fine in most of the case, the logic
is broken for big-endian 32-bit kernels.

When reading a u64 mask using (u32 *)(&val)[0], find_*_bit() assumes
that it gets the lower 32 bits of u64, but instead it gets the upper
32 bits - which is wrong.

The fix is to swap the words of the u64 to handle this case.
This is _not_ a regular endianness swap.

Suggested-by: Yury Norov <ynorov@...iumnetworks.com>
Signed-off-by: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Yury Norov <ynorov@...iumnetworks.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: linuxppc-dev@...ts.ozlabs.org
Link: http://lkml.kernel.org/r/1471426568-31051-2-git-send-email-maddy@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/bitmap.h | 18 ++++++++++++++++++
 kernel/events/core.c   |  5 +++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 598bc99..3b77588 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -339,6 +339,24 @@ static inline int bitmap_parse(const char *buf, unsigned int buflen,
 	return __bitmap_parse(buf, buflen, 0, maskp, nmaskbits);
 }
 
+/*
+ * bitmap_from_u64 - Check and swap words within u64.
+ *  @mask: source bitmap
+ *  @dst:  destination bitmap
+ *
+ * In 32-bit Big Endian kernel, when using (u32 *)(&val)[*]
+ * to read u64 mask, we will get the wrong word.
+ * That is "(u32 *)(&val)[0]" gets the upper 32 bits,
+ * but we expect the lower 32-bits of u64.
+ */
+static inline void bitmap_from_u64(unsigned long *dst, u64 mask)
+{
+	dst[0] = mask & ULONG_MAX;
+
+	if (sizeof(mask) > sizeof(unsigned long))
+		dst[1] = mask >> 32;
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __LINUX_BITMAP_H */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ca4fde5..849919c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5340,9 +5340,10 @@ perf_output_sample_regs(struct perf_output_handle *handle,
 			struct pt_regs *regs, u64 mask)
 {
 	int bit;
+	DECLARE_BITMAP(_mask, 64);
 
-	for_each_set_bit(bit, (const unsigned long *) &mask,
-			 sizeof(mask) * BITS_PER_BYTE) {
+	bitmap_from_u64(_mask, mask);
+	for_each_set_bit(bit, _mask, sizeof(mask) * BITS_PER_BYTE) {
 		u64 val;
 
 		val = perf_reg_value(regs, bit);