[PATCH v2] EDAC/amd64: Only translate Node ID if GPU nodes are present

[Phineas Su]

The fixup_node_id() function adjusts the AMD Node ID for GPU memory
controllers (which report as SMCA_UMC_V2) on heterogeneous systems.
CPU memory controllers typically report as SMCA_UMC (v1) and do not
require translation.

If a CPU memory controller on a CPU-only system were to report as
SMCA_UMC_V2 (e.g. due to future hardware iterations, firmware reporting,
or kernel enumeration differences), the code would attempt to apply the
GPU translation. Since gpu_node_map is uninitialized on CPU-only systems,
this would lead to an unintended translation being applied.

Harden the translation logic by checking that GPU nodes are actually
present in the system (gpu_node_map.node_count > 0) before applying the
translation. This ensures CPU-only systems are always safely bypassed.

Signed-off-by: Phineas Su <pohaosu@xxxxxxxxxx>
---
v2:
  - Reframed commit message to focus on robustness rather than a confirmed
    bug, as Zen4 CPUs do not generally report UMC_V2. (Yazen)

 drivers/edac/amd64_edac.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/edac/amd64_edac.c b/drivers/edac/amd64_edac.c
index c6aa69dbd9fb..1e688123a50c 100644
--- a/drivers/edac/amd64_edac.c
+++ b/drivers/edac/amd64_edac.c
@@ -1047,6 +1047,10 @@ static int fixup_node_id(int node_id, struct mce *m)
 	if (smca_get_bank_type(m->extcpu, m->bank) != SMCA_UMC_V2)
 		return node_id;
 
+	/* If no GPU nodes are present, no fixup is needed. */
+	if (!gpu_node_map.node_count)
+		return node_id;
+
 	/* Nodes below the GPU base node are CPU nodes and don't need a fixup. */
 	if (nid < gpu_node_map.base_node_id)
 		return node_id;
-- 
2.54.0.1136.gdb2ca164c4-goog