On Fri, 29 Aug 2025 15:29:06 -0700 Dave Jiang dave.jiang@intel.com wrote:
The current implementation of CXL memory hotplug notifier gets called before the HMAT memory hotplug notifier. The CXL driver calculates the access coordinates (bandwidth and latency values) for the CXL end to end path (i.e. CPU to endpoint). When the CXL region is onlined, the CXL memory hotplug notifier writes the access coordinates to the HMAT target structs. Then the HMAT memory hotplug notifier is called and it creates the access coordinates for the node sysfs attributes.
During testing on an Intel platform, it was found that although the newly calculated coordinates were pushed to sysfs, the sysfs attributes for the access coordinates showed up with the wrong initiator. The system has 4 nodes (0, 1, 2, 3) where node 0 and 1 are CPU nodes and node 2 and 3 are CXL nodes. The expectation is that node 2 would show up as a target to node 0: /sys/devices/system/node/node2/access0/initiators/node0
However it was observed that node 2 showed up as a target under node 1: /sys/devices/system/node/node2/access0/initiators/node1
The original intent of the 'ext_updated' flag in HMAT handling code was to stop HMAT memory hotplug callback from clobbering the access coordinates after CXL has injected its calculated coordinates and replaced the generic target access coordinates provided by the HMAT table in the HMAT target structs. However the flag is hacky at best and blocks the updates from other CXL regions that are onlined in the same node later on. Remove the 'ext_updated' flag usage and just update the access coordinates for the nodes directly without touching HMAT target data.
The hotplug memory callback ordering is changed. Instead of changing CXL, move HMAT back so there's room for the levels rather than have CXL share the same level as SLAB_CALLBACK_PRI. The change will resulting in the CXL callback to be executed after the HMAT callback.
With the change, the CXL hotplug memory notifier runs after the HMAT callback. The HMAT callback will create the node sysfs attributes for access coordinates. The CXL callback will write the access coordinates to the now created node sysfs attributes directly and will not pollute the HMAT target values.
A nodemask is introduced to keep track if a node has been updated and prevents further updates.
Fixes: 067353a46d8c ("cxl/region: Add memory hotplug notifier for cxl region") Cc: stable@vger.kernel.org Tested-by: Marc Herbert marc.herbert@linux.intel.com Reviewed-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Dave Jiang dave.jiang@intel.com
Reviewed-by: Jonathan Cameron jonathan.cameron@huawei.com