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Subject[tip: perf/urgent] perf/x86/intel/bts: Fix the use of page_private()
The following commit has been merged into the perf/urgent branch of tip:

Commit-ID: ff61541cc6c1962957758ba433c574b76f588d23
Gitweb: https://git.kernel.org/tip/ff61541cc6c1962957758ba433c574b76f588d23
Author: Alexander Shishkin <alexander.shishkin@linux.intel.com>
AuthorDate: Thu, 05 Dec 2019 17:28:52 +03:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 17 Dec 2019 13:32:46 +01:00

perf/x86/intel/bts: Fix the use of page_private()

Commit

8062382c8dbe2 ("perf/x86/intel/bts: Add BTS PMU driver")

brought in a warning with the BTS buffer initialization
that is easily tripped with (assuming KPTI is disabled):

instantly throwing:

> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 326 at arch/x86/events/intel/bts.c:86 bts_buffer_setup_aux+0x117/0x3d0
> Modules linked in:
> CPU: 2 PID: 326 Comm: perf Not tainted 5.4.0-rc8-00291-gceb9e77324fa #904
> RIP: 0010:bts_buffer_setup_aux+0x117/0x3d0
> Call Trace:
> rb_alloc_aux+0x339/0x550
> perf_mmap+0x607/0xc70
> mmap_region+0x76b/0xbd0
...

It appears to assume (for lost raisins) that PagePrivate() is set,
while later it actually tests for PagePrivate() before using
page_private().

Make it consistent and always check PagePrivate() before using
page_private().

Fixes: 8062382c8dbe2 ("perf/x86/intel/bts: Add BTS PMU driver")
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lkml.kernel.org/r/20191205142853.28894-2-alexander.shishkin@linux.intel.com
---
arch/x86/events/intel/bts.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 38de4a7..6a3b599 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -63,9 +63,17 @@ struct bts_buffer {

static struct pmu bts_pmu;

+static int buf_nr_pages(struct page *page)
+{
+ if (!PagePrivate(page))
+ return 1;
+
+ return 1 << page_private(page);
+}
+
static size_t buf_size(struct page *page)
{
- return 1 << (PAGE_SHIFT + page_private(page));
+ return buf_nr_pages(page) * PAGE_SIZE;
}

static void *
@@ -83,9 +91,7 @@ bts_buffer_setup_aux(struct perf_event *event, void **pages,
/* count all the high order buffers */
for (pg = 0, nbuf = 0; pg < nr_pages;) {
page = virt_to_page(pages[pg]);
- if (WARN_ON_ONCE(!PagePrivate(page) && nr_pages > 1))
- return NULL;
- pg += 1 << page_private(page);
+ pg += buf_nr_pages(page);
nbuf++;
}

@@ -109,7 +115,7 @@ bts_buffer_setup_aux(struct perf_event *event, void **pages,
unsigned int __nr_pages;

page = virt_to_page(pages[pg]);
- __nr_pages = PagePrivate(page) ? 1 << page_private(page) : 1;
+ __nr_pages = buf_nr_pages(page);
buf->buf[nbuf].page = page;
buf->buf[nbuf].offset = offset;
buf->buf[nbuf].displacement = (pad ? BTS_RECORD_SIZE - pad : 0);
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