Hi Jonathan,

On 1/5/26 18:07, Jonathan Cameron wrote:

On Fri, 19 Dec 2025 18:11:24 +0000
Ben Horgan [off-list ref] wrote:

quoted

From: James Morse <james.morse@arm.com>

Intel RDT's CDP feature allows the cache to use a different control value
depending on whether the accesses was for instruction fetch or a data
access. MPAM's equivalent feature is the other way up: the CPU assigns a
different partid label to traffic depending on whether it was instruction
fetch or a data access, which causes the cache to use a different control
value based solely on the partid.

MPAM can emulate CDP, with the side effect that the alternative partid is
seen by all MSC, it can't be enabled per-MSC.

Add the resctrl hooks to turn this on or off. Add the helpers that match a
closid against a task, which need to be aware that the value written to
hardware is not the same as the one resctrl is using.

Update the 'arm64_mpam_global_default' variable the arch code uses during
context switch to know when the per-cpu value should be used instead.

Awkwardly, the MB controls don't implement CDP. To emulate this, the MPAM
equivalent needs programming twice by the resctrl glue, as resctrl expects
the bandwidth controls to be applied independently for both data and
instruction-fetch.

CC: Dave Martin <Dave.Martin@arm.com>
CC: Amit Singh Tomar <redacted>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>

Minor thing below.
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

quoted

diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index 5a78299ec464..ba0312b55d9f 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h

@@ -5,6 +5,7 @@
 #define __LINUX_ARM_MPAM_H
 
 #include <linux/acpi.h>
+#include <linux/resctrl_types.h>

This seems odd as nothing added to the header in this path appears to need it.
Maybe should be down in the c file or in a different patch?

Yep, moved it to patch 33, arm_mpam: resctrl: Allow resctrl to allocate
monitors.

quoted

 #include <linux/types.h>
 
 struct mpam_msc;

@@ -56,6 +57,8 @@ void resctrl_arch_set_cpu_default_closid(int cpu, u32 closid);
 void resctrl_arch_set_closid_rmid(struct task_struct *tsk, u32 closid, u32 rmid);
 void resctrl_arch_set_cpu_default_closid_rmid(int cpu, u32 closid, u32 rmid);
 void resctrl_arch_sched_in(struct task_struct *tsk);
+bool resctrl_arch_match_closid(struct task_struct *tsk, u32 closid);
+bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 closid, u32 rmid);
 
 /**
  * mpam_register_requestor() - Register a requestor with the MPAM driver

Thanks,

Ben