Commit ff61541c authored Dec 05, 2019 by Alexander Shishkin Committed by Peter Zijlstra Dec 17, 2019

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



Commit

  8062382c ("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: 8062382c ("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

parent 1e69a0ef

arch/x86/events/intel/bts.c

+11 −5

Original line number	Diff line number	Diff line
		@@ -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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