[PATCH 6.10 225/809] perf: Fix default aux_watermark calculation

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6.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Adrian Hunter <adrian.hunter@xxxxxxxxx>

[ Upstream commit 43deb76b19663a96ec2189d8f4eb9a9dc2d7623f ]

The default aux_watermark is half the AUX area buffer size. In general,
on a 64-bit architecture, the AUX area buffer size could be a bigger than
fits in a 32-bit type, but the calculation does not allow for that
possibility.

However the aux_watermark value is recorded in a u32, so should not be
more than U32_MAX either.

Fix by doing the calculation in a correctly sized type, and limiting the
result to U32_MAX.

Fixes: d68e6799a5c8 ("perf: Cap allocation order at aux_watermark")
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240624201101.60186-7-adrian.hunter@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/events/ring_buffer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 4013408ce0123..485cf0a66631b 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -688,7 +688,9 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
 		 * max_order, to aid PMU drivers in double buffering.
 		 */
 		if (!watermark)
-			watermark = nr_pages << (PAGE_SHIFT - 1);
+			watermark = min_t(unsigned long,
+					  U32_MAX,
+					  (unsigned long)nr_pages << (PAGE_SHIFT - 1));
 
 		/*
 		 * Use aux_watermark as the basis for chunking to
-- 
2.43.0







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