comment about MAX_CPUS

Author: braindigitalis

src/idt.c

@@ -15,7 +15,19 @@
 
 #define MSI_VECTORS 256
 #define FIRST_MSI_VECTOR 64
-#define MSI_WORDS (MSI_VECTORS / 64U)
+#define MSI_WORDS (MSI_VECTORS / 64)
+
+/**
+ * @note MAX_CPUS is set to 256 (not the expected physical core count).
+ *
+ * Local APIC IDs are 8-bit fields (0–255) and are not guaranteed to be
+ * sequential, zero-based, or densely packed. Some systems leave gaps
+ * in the LAPIC ID space or assign non-zero IDs to the bootstrap CPU.
+ *
+ * By sizing arrays to 256, we can index directly by LAPIC ID without
+ * needing an LAPIC->OS CPU remapping table. This avoids subtle bugs on
+ * odd hardware at the cost of a small amount of extra memory.
+ */
 #define MAX_CPUS 256
 
 /* Precompute reserved mask for the first word */