x86/resctrl: Add max_bw to struct resctrl_membw

__rdt_get_mem_config_amd() and __get_mem_config_intel() both use the
default_ctrl property as a maximum value. This is because the MBA schema works
differently between these platforms. Doing this complicates determining
whether the default_ctrl property belongs to the arch code, or can be derived
from the schema format.

Deriving the maximum or default value from the schema format would avoid the
architecture code having to tell resctrl such obvious things as the maximum
percentage is 100, and the maximum bitmap is all ones.

Maximum bandwidth is always going to vary per platform. Add max_bw as
a special case. This is currently used for the maximum MBA percentage on Intel
platforms, but can be removed from the architecture code if 'percentage'
becomes a schema format resctrl supports directly.

This value isn't needed for other schema formats.

This will allow the default_ctrl to be generated from the schema properties
when it is needed.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Amit Singh Tomar <amitsinght@marvell.com> # arm64
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com> # arm64
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20250311183715.16445-8-james.morse@arm.com

Author: James Morse

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

@@ -212,6 +212,7 @@ static __init bool __get_mem_config_intel(struct rdt_resource *r)
 	hw_res->num_closid = edx.split.cos_max + 1;
 	max_delay = eax.split.max_delay + 1;
 	r->default_ctrl = MAX_MBA_BW;
+	r->membw.max_bw = MAX_MBA_BW;
 	r->membw.arch_needs_linear = true;
 	if (ecx & MBA_IS_LINEAR) {
 		r->membw.delay_linear = true;
@@ -250,6 +251,7 @@ static __init bool __rdt_get_mem_config_amd(struct rdt_resource *r)
 	cpuid_count(0x80000020, subleaf, &eax, &ebx, &ecx, &edx);
 	hw_res->num_closid = edx + 1;
 	r->default_ctrl = 1 << eax;
+	r->membw.max_bw = 1 << eax;
 
 	/* AMD does not use delay */
 	r->membw.delay_linear = false;

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

@@ -63,9 +63,9 @@ static bool bw_validate(char *buf, u32 *data, struct rdt_resource *r)
 		return true;
 	}
 
-	if (bw < r->membw.min_bw || bw > r->default_ctrl) {
+	if (bw < r->membw.min_bw || bw > r->membw.max_bw) {
 		rdt_last_cmd_printf("MB value %u out of range [%d,%d]\n",
-				    bw, r->membw.min_bw, r->default_ctrl);
+				    bw, r->membw.min_bw, r->membw.max_bw);
 		return false;
 	}
 

include/linux/resctrl.h

@@ -165,6 +165,7 @@ enum membw_throttle_mode {
 /**
  * struct resctrl_membw - Memory bandwidth allocation related data
  * @min_bw:		Minimum memory bandwidth percentage user can request
+ * @max_bw:		Maximum memory bandwidth value, used as the reset value
  * @bw_gran:		Granularity at which the memory bandwidth is allocated
  * @delay_linear:	True if memory B/W delay is in linear scale
  * @arch_needs_linear:	True if we can't configure non-linear resources
@@ -175,6 +176,7 @@ enum membw_throttle_mode {
  */
 struct resctrl_membw {
 	u32				min_bw;
+	u32				max_bw;
 	u32				bw_gran;
 	u32				delay_linear;
 	bool				arch_needs_linear;