x86/resctrl: Abstract and use supports_mba_mbps()

To determine whether the mba_MBps option to resctrl should be supported,
resctrl tests the boot CPUs' x86_vendor.

This isn't portable, and needs abstracting behind a helper so this check
can be part of the filesystem code that moves to /fs/.

Re-use the tests set_mba_sc() does to determine if the mba_sc is supported
on this system. An 'alloc_capable' test is added so that support for the
controls isn't implied by the 'delay_linear' property, which is always
true for MPAM. Because mbm_update() only update mba_sc if the mbm_local
counters are enabled, supports_mba_mbps() checks is_mbm_local_enabled().
(instead of using is_mbm_enabled(), which checks both).
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jamie Iles <quic_jiles@quicinc.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20220902154829.30399-8-james.morse@arm.com

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

@@ -1890,17 +1890,26 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r)
 }
 
 /*
- * Enable or disable the MBA software controller
- * which helps user specify bandwidth in MBps.
  * MBA software controller is supported only if
  * MBM is supported and MBA is in linear scale.
  */
+static bool supports_mba_mbps(void)
+{
+	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
+
+	return (is_mbm_local_enabled() &&
+		r->alloc_capable && is_mba_linear());
+}
+
+/*
+ * Enable or disable the MBA software controller
+ * which helps user specify bandwidth in MBps.
+ */
 static int set_mba_sc(bool mba_sc)
 {
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
 
-	if (!is_mbm_enabled() || !is_mba_linear() ||
-	    mba_sc == is_mba_sc(r))
+	if (!supports_mba_mbps() || mba_sc == is_mba_sc(r))
 		return -EINVAL;
 
 	r->membw.mba_sc = mba_sc;
@@ -2255,7 +2264,7 @@ static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		ctx->enable_cdpl2 = true;
 		return 0;
 	case Opt_mba_mbps:
-		if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+		if (!supports_mba_mbps())
 			return -EINVAL;
 		ctx->enable_mba_mbps = true;
 		return 0;