Patch "perf/x86/intel/bts: Fix the use of page_private()" has been added to the 4.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-x86-intel-bts-fix-the-use-of-page_private.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 77a01f7b59e6a95e155456622d0157123f4e323f
Author: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Date:   Thu Dec 5 17:28:52 2019 +0300

    perf/x86/intel/bts: Fix the use of page_private()
    
    [ Upstream commit ff61541cc6c1962957758ba433c574b76f588d23 ]
    
    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@xxxxxxxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
    Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
    Cc: Ingo Molnar <mingo@xxxxxxxxxx>
    Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
    Link: https://lkml.kernel.org/r/20191205142853.28894-2-alexander.shishkin@xxxxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 24ffa1e88cf9..4d3399405d06 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -71,9 +71,17 @@ 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 *
@@ -89,9 +97,7 @@ bts_buffer_setup_aux(int cpu, void **pages, int nr_pages, bool overwrite)
 	/* 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++;
 	}
 
@@ -115,7 +121,7 @@ bts_buffer_setup_aux(int cpu, void **pages, int nr_pages, bool overwrite)
 		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);