On 01/08/2025 15:35, Ryan Roberts wrote:

[...]

quoted

@@ -1366,7 +1648,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
 
 	VM_BUG_ON(!mhp_range_allowed(start, size, true));
 
-	if (can_set_direct_map())
+	if (force_pte_mapping() ||
+	    (linear_map_requires_bbml2 && !system_supports_bbml2_noabort()))

So force_pte_mapping() isn't actually returning what it sounds like it is; it's
returning whether you would have to force pte mapping based on the current cpu's
support for bbml2. Perhaps it would be better to implement force_pte_mapping()  as:

static inline bool force_pte_mapping(void)
{
	bool bbml2 = (system_capabilities_finalized() &&
			system_supports_bbml2_noabort()) ||
			bbml2_noabort_available();

Sorry that should have been:

	bool bbml2 = system_capabilities_finalized() ?
		system_supports_bbml2_noabort() : bbml2_noabort_available();

	return (!bbml2 && (rodata_full || arm64_kfence_can_set_direct_map() ||
			   is_realm_world())) ||
		debug_pagealloc_enabled();
}