[PATCH v2] cxl/events: Test CME counter expiry with equality, not bitwise AND

[Guixin Liu <kanie@linux.alibaba.com>]

The Memory Event Type field in the General Media and DRAM event records
is an enumeration, not a bitmask. The validity checks for the advanced
programmable CME counter expiration event (05h) test the field with a
bitwise AND, so types 01h, 03h, 04h and 06h match it as well.

A device reporting one of those types trips WARN_ON_ONCE once the
general media or DRAM tracepoint is enabled, which is the case anywhere
rasdaemon collects CXL events. Under panic_on_warn=1 that kills the
machine.

Compare the type field for equality instead. Type 05h records that do
violate the spec conditions still warn.

Fixes: cd3b36cfc659 ("cxl/events: Add extra validity checks for corrected memory error count in General Media Event Record")
Fixes: d8145bb8af5c ("cxl/events: Add extra validity checks for CVME count in DRAM Event Record")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---
Found by code inspection during review of a downstream backport of
these two patches. Reproduced in a QEMU CXL topology by injecting
General Media events through the cxl-inject-general-media-event QMP
command: a type 01h event warns in cxl_event_trace_record() without
the fix and is traced without a warning with it; type 05h events that
violate the spec conditions still warn.

Changes since v1 [1]:
- Collect the commit log suggested by Dave Jiang and the subject
  suggested by Alison Schofield.
- Move the reproducer explanation below '---' (Dave Jiang).
- Add the 'Assisted-by: LLM' tag (Dave Jiang).

[1]: https://lore.kernel.org/all/20260921120932.1769566-1-kanie@linux.alibaba.com/

 drivers/cxl/core/mbox.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index 55828a836c01..01341f524a93 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -942,11 +942,11 @@ void cxl_event_trace_record(struct cxl_memdev *cxlmd,
 
 			if (evt->gen_media.media_hdr.descriptor &
 			    CXL_GMER_EVT_DESC_THRESHOLD_EVENT)
-				WARN_ON_ONCE((evt->gen_media.media_hdr.type &
+				WARN_ON_ONCE((evt->gen_media.media_hdr.type ==
 					      CXL_GMER_MEM_EVT_TYPE_AP_CME_COUNTER_EXPIRE) &&
 					     !get_unaligned_le24(evt->gen_media.cme_count));
 			else
-				WARN_ON_ONCE(evt->gen_media.media_hdr.type &
+				WARN_ON_ONCE(evt->gen_media.media_hdr.type ==
 					     CXL_GMER_MEM_EVT_TYPE_AP_CME_COUNTER_EXPIRE);
 
 			trace_cxl_general_media(cxlmd, type, cxlr, hpa,
@@ -957,11 +957,11 @@ void cxl_event_trace_record(struct cxl_memdev *cxlmd,
 
 			if (evt->dram.media_hdr.descriptor &
 			    CXL_GMER_EVT_DESC_THRESHOLD_EVENT)
-				WARN_ON_ONCE((evt->dram.media_hdr.type &
+				WARN_ON_ONCE((evt->dram.media_hdr.type ==
 					      CXL_DER_MEM_EVT_TYPE_AP_CME_COUNTER_EXPIRE) &&
 					     !get_unaligned_le24(evt->dram.cvme_count));
 			else
-				WARN_ON_ONCE(evt->dram.media_hdr.type &
+				WARN_ON_ONCE(evt->dram.media_hdr.type ==
 					     CXL_DER_MEM_EVT_TYPE_AP_CME_COUNTER_EXPIRE);
 
 			trace_cxl_dram(cxlmd, type, cxlr, hpa, hpa_alias,
-- 
2.43.7