[tip: x86/cache] x86,fs/resctrl: Add resctrl_arch_preconvert_bw()

[tip-bot2 for Dave Martin]

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     57a354d20a01287bd173b13231eb5afcda337eee
Gitweb:        https://git.kernel.org/tip/57a354d20a01287bd173b13231eb5afcda337eee
Author:        Dave Martin <dave.martin@xxxxxxx>
AuthorDate:    Fri, 11 Sep 2026 17:36:11 +01:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Mon, 14 Sep 2026 08:15:11 -07:00

x86,fs/resctrl: Add resctrl_arch_preconvert_bw()

On MPAM systems the rounding behaviour of the MBA control would be improved if
the rounding in the fs/resctrl code is removed but this is not the case for
x86. To allow any rounding or conversion of the bandwidth value provided by
the user to be specified by the arch code a new arch hook is required.

Introduce resctrl_arch_preconvert_bw(), and add its x86 implementation.
This is currently unused in resctrl but when plumbed in it will replace the
call to roundup() in bw_validate().

Signed-off-by: Dave Martin <dave.martin@xxxxxxx>
Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
Link: https://patch.msgid.link/20260911163613.1131447-2-ben.horgan@xxxxxxx
---
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  6 ++++++
 include/linux/resctrl.h                   | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index e74f1ed..6204448 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -16,9 +16,15 @@
 #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
 
 #include <linux/cpu.h>
+#include <linux/math.h>
 
 #include "internal.h"
 
+u32 resctrl_arch_preconvert_bw(const struct rdt_resource *r, u32 val)
+{
+	return roundup(val, (unsigned long)r->membw.bw_gran);
+}
+
 int resctrl_arch_update_one(struct rdt_resource *r, struct rdt_ctrl_domain *d,
 			    u32 closid, enum resctrl_conf_type t, u32 cfg_val)
 {
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index dd09c2c..10dfdca 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -505,6 +505,25 @@ bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r);
  */
 int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable);
 
+/**
+ * resctrl_arch_preconvert_bw() - Prepare bandwidth control value for arch use.
+ * @r:		Resource whose schema was written.
+ * @val:	Bandwidth control value written to the schemata file by userspace.
+ *
+ * Convert the user provided bandwidth control value to an appropriate form for
+ * consumption by the hardware driver for resource @r. Converted value is stored
+ * in rdt_ctrl_domain::staged_config[] for later consumption by
+ * resctrl_arch_update_domains(). Is not called when MBA software controller is
+ * enabled.
+ *
+ * Architectures for which this pre-conversion hook is not useful should supply
+ * an implementation of this function that just returns @val unmodified.
+ *
+ * Return:
+ * The converted value.
+ */
+u32 resctrl_arch_preconvert_bw(const struct rdt_resource *r, u32 val);
+
 /*
  * Update the ctrl_val and apply this config right now.
  * Must be called on one of the domain's CPUs.