x86/resctrl: Fix arch_mbm_* array overrun on SNC

When using resctrl on systems with Sub-NUMA Clustering enabled, monitoring
groups may be allocated RMID values which would overrun the
arch_mbm_{local,total} arrays.

This is due to inconsistencies in whether the SNC-adjusted num_rmid value or
the unadjusted value in resctrl_arch_system_num_rmid_idx() is used. The
num_rmid value for the L3 resource is currently:

  resctrl_arch_system_num_rmid_idx() / snc_nodes_per_l3_cache

As a simple fix, make resctrl_arch_system_num_rmid_idx() return the
SNC-adjusted, L3 num_rmid value on x86.

Fixes: e13db55 ("x86/resctrl: Introduce snc_nodes_per_l3_cache")
Signed-off-by: Peter Newman <peternewman@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/20240822190212.1848788-1-peternewman@google.com

arch/x86/include/asm/resctrl.h

@@ -156,12 +156,6 @@ static inline void resctrl_sched_in(struct task_struct *tsk)
 		__resctrl_sched_in(tsk);
 }
 
-static inline u32 resctrl_arch_system_num_rmid_idx(void)
-{
-	/* RMID are independent numbers for x86. num_rmid_idx == num_rmid */
-	return boot_cpu_data.x86_cache_max_rmid + 1;
-}
-
 static inline void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
 {
 	*rmid = idx;

arch/x86/kernel/cpu/resctrl/core.c

@@ -119,6 +119,14 @@ struct rdt_hw_resource rdt_resources_all[] = {
 	},
 };
 
+u32 resctrl_arch_system_num_rmid_idx(void)
+{
+	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
+
+	/* RMID are independent numbers for x86. num_rmid_idx == num_rmid */
+	return r->num_rmid;
+}
+
 /*
  * cache_alloc_hsw_probe() - Have to probe for Intel haswell server CPUs
  * as they do not have CPUID enumeration support for Cache allocation.

include/linux/resctrl.h

@@ -248,6 +248,7 @@ struct resctrl_schema {
 
 /* The number of closid supported by this resource regardless of CDP */
 u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
+u32 resctrl_arch_system_num_rmid_idx(void);
 int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
 
 /*