x86/resctrl: Support CPUID enumeration of MBM counter width

The original Memory Bandwidth Monitoring (MBM) architectural
definition defines counters of up to 62 bits in the
IA32_QM_CTR MSR while the first-generation MBM implementation
uses statically defined 24 bit counters.

Expand the MBM CPUID enumeration properties to include the MBM
counter width. The previously undefined EAX output register contains,
in bits [7:0], the MBM counter width encoded as an offset from
24 bits. Enumerating this property is only specified for Intel
CPUs.

Suggested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/afa3af2f753f6bc301fb743bc8944e749cb24afa.1588715690.git.reinette.chatre@intel.com

arch/x86/include/asm/processor.h

@@ -113,9 +113,10 @@ struct cpuinfo_x86 {
 	/* in KB - valid for CPUS which support this call: */
 	unsigned int		x86_cache_size;
 	int			x86_cache_alignment;	/* In bytes */
-	/* Cache QoS architectural values: */
+	/* Cache QoS architectural values, valid only on the BSP: */
 	int			x86_cache_max_rmid;	/* max index */
 	int			x86_cache_occ_scale;	/* scale to bytes */
+	int			x86_cache_mbm_width_offset;
 	int			x86_power;
 	unsigned long		loops_per_jiffy;
 	/* cpuid returned max cores value: */

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

@@ -964,6 +964,7 @@ void resctrl_cpu_detect(struct cpuinfo_x86 *c)
 	if (!cpu_has(c, X86_FEATURE_CQM_LLC)) {
 		c->x86_cache_max_rmid  = -1;
 		c->x86_cache_occ_scale = -1;
+		c->x86_cache_mbm_width_offset = -1;
 		return;
 	}
 
@@ -980,6 +981,10 @@ void resctrl_cpu_detect(struct cpuinfo_x86 *c)
 
 		c->x86_cache_max_rmid  = ecx;
 		c->x86_cache_occ_scale = ebx;
+		if (c->x86_vendor == X86_VENDOR_INTEL)
+			c->x86_cache_mbm_width_offset = eax & 0xff;
+		else
+			c->x86_cache_mbm_width_offset = -1;
 	}
 }