Changes in v3: - Introduce numa_add_reserved_memblk() - Use more explicit way to make sure CFMWs fake node >= 1 - Replace numa_add_memblk() with numa_add_reserved_memblk() in acpi_parse_cfmws() Problem ------- The absence of SRAT would cause the fake_pxm to be -1 and increment to 0, then send to acpi_parse_cfmws(). If there exists CXL memory ranges that are defined in the CFMWS and not already defined in the SRAT, the new node (node0) for the CXL memory would be invalid, as node0 is already in "used", and all CXL memory might be online on node0. Control cxl fake node value --------------------------- This utilizes node_set(0, nodes_found_map) to set pxm&node map. With this setting, acpi_map_pxm_to_node() could return the expected node value even if no SRAT. numa_add_memblk() problem on this issue --------------------------------------- If SRAT is valid, the numa_memblks_init() would then utilize numa_move_tail_memblk() to move the numa_memblk from numa_meminfo to numa_reserved_meminfo in CFMWs fake node situation. If SRAT is missing or bad, the numa_memblks_init() would fail since init_func() would fail. And it causes that no numa_memblk in numa_reserved_meminfo list and the following dax_cxl driver could find the expected fake node. numa_add_reserved_memblk() -------------------------- Use numa_add_reserved_memblk() to replace numa_add_memblk(), since the cxl numa_memblk added by numa_add_memblk() would finally be moved to numa_reserved_meminfo, and numa_add_reserved_memblk() here could add cxl numa_memblk into reserved list directly. Hence, no matter SRAT is good or not, cxl numa_memblk could be allocated to reserved list. dax_kmem problem ---------------- The dax_kmem driver will fail if no SRAT because something wrong in memory_group_register_static(). The good result is our cxl memory would not be assigned to node0 anymore! Discussion ---------- As papering these things looks like not easily, in v2 patch[1] I chose to aggressively fail the acpi_parse_cfmws() in srat.c since it mainly works for building cxl fake nodes and also fail the CXL init in cxl_acpi_probe per the discussion from Jonathan[2]. Actually, I am not sure if this(v3) is the best way to handle this issue, so hopes more comments to guide me! Link: [1] https://lore.kernel.org/linux-cxl/Z9RfnXQlr9G1qz00@xxxxxxxxxxxxxxxxxx/T/#t [2] https://lists.nongnu.org/archive/html/qemu-devel/2025-03/msg03668.html Yuquan Wang (2): mm: numa_memblks: introduce numa_add_reserved_memblk ACPI: NUMA: debug invalid unused PXM value for CFMWs drivers/acpi/numa/srat.c | 11 ++++++++--- include/linux/numa_memblks.h | 1 + mm/numa_memblks.c | 16 ++++++++++++++++ 3 files changed, 25 insertions(+), 3 deletions(-) -- 2.34.1
