This is the missing piece to make MPAM usable resctrl in user-space. This has
shed its debugfs code and the read/write 'event configuration' for the monitors
to make the series smaller.

This adds the arch code and KVM support first. I anticipate the whole thing
going via arm64, but if goes via tip instead, the an immutable branch with those
patches should be easy to do.

I've not CC'd all the relevant maintainers because its the merge window.
(...and yet there are folk chomping at the bit to see this posted...)


Generally the resctrl glue code works by picking what MPAM features it can expose
from the MPAM drive, then configuring the structs that back the resctrl helpers.
If your platform is sufficiently Xeon shaped, you should be able to get L2/L3 CPOR
bitmaps exposed via resctrl. CSU counters work if they are on/after the L3. MBWU
counters are considerably more hairy, and depend on hueristics around the topology,
and a bunch of stuff trying to emulate ABMC.
If it didn't pick what you wanted it to, please share the debug messages produced
when enabling dynamic debug and booting with:
| dyndbg="file mpam_resctrl.c +pl"

I've not found a platform that can test all the behaviours around the monitors,
so this is where I'd expect the most bugs.

The MPAM spec that describes all the system and MMIO registers can be found here:
https://developer.arm.com/documentation/ddi0598/db/?lang=en
(Ignored the 'RETIRED' warning - that is just arm moving the documentation around.
 This document has the best overview)


This series is based on arm64/for-next/core, and can be retrieved from:
https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/glue/rfc

There is no snapshot branch - this is it!
I'll push the extras branch once I've gotten a handle on the DT shaped mess in
there.

What is MPAM? Set your time-machine to 2020:
https://lore.kernel.org/lkml/20201030161120.227225-1-james.morse@arm.com/


Thanks,

James Morse (32):
  arm64: mpam: Context switch the MPAM registers
  arm64: mpam: Re-initialise MPAM regs when CPU comes online
  arm64: mpam: Advertise the CPUs MPAM limits to the driver
  arm64: mpam: Add cpu_pm notifier to restore MPAM sysregs
  arm64: mpam: Add helpers to change a task or cpu's MPAM PARTID/PMG
    values
  KVM: arm64: Force guest EL1 to use user-space's partid configuration
  arm_mpam: resctrl: Add boilerplate cpuhp and domain allocation
  arm_mpam: resctrl: Pick the caches we will use as resctrl resources
  arm_mpam: resctrl: Implement resctrl_arch_reset_all_ctrls()
  arm_mpam: resctrl: Add resctrl_arch_get_config()
  arm_mpam: resctrl: Implement helpers to update configuration
  arm_mpam: resctrl: Add plumbing against arm64 task and cpu hooks
  arm_mpam: resctrl: Add CDP emulation
  arm_mpam: resctrl: Add rmid index helpers
  arm_mpam: resctrl: Add support for 'MB' resource
  arm_mpam: resctrl: Add support for csu counters
  arm_mpam: resctrl: pick classes for use as mbm counters
  arm_mpam: resctrl: Pre-allocate free running monitors
  arm_mpam: resctrl: Pre-allocate assignable monitors
  arm_mpam: resctrl: Add kunit test for ABMC/CDP interactions
  arm_mpam: resctrl: Add resctrl_arch_config_cntr() for ABMC use
  arm_mpam: resctrl: Allow resctrl to allocate monitors
  arm_mpam: resctrl: Add resctrl_arch_rmid_read() and
    resctrl_arch_reset_rmid()
  arm_mpam: resctrl: Add resctrl_arch_cntr_read() &
    resctrl_arch_reset_cntr()
  arm_mpam: resctrl: Add empty definitions for assorted resctrl
    functions
  arm64: mpam: Select ARCH_HAS_CPU_RESCTRL
  arm_mpam: resctrl: Call resctrl_init() on platforms that can support
    resctrl
  arm_mpam: resctrl: Call resctrl_exit() in the event of errors
  arm_mpam: resctrl: Update the rmid reallocation limit
  arm_mpam: resctrl: Sort the order of the domain lists
  arm_mpam: Generate a configuration for min controls
  arm_mpam: Quirk CMN-650's CSU NRDY behaviour

Dave Martin (2):
  arm_mpam: resctrl: Convert to/from MPAMs fixed-point formats
  arm_mpam: resctrl: Add kunit test for control format conversions

Shanker Donthineni (4):
  arm_mpam: Add quirk framework
  arm_mpam: Add workaround for T241-MPAM-1
  arm_mpam: Add workaround for T241-MPAM-4
  arm_mpam: Add workaround for T241-MPAM-6

 Documentation/arch/arm64/silicon-errata.rst |    9 +
 arch/arm64/Kconfig                          |    6 +-
 arch/arm64/include/asm/kvm_host.h           |    1 +
 arch/arm64/include/asm/mpam.h               |  105 +
 arch/arm64/include/asm/resctrl.h            |    2 +
 arch/arm64/include/asm/thread_info.h        |    3 +
 arch/arm64/kernel/Makefile                  |    1 +
 arch/arm64/kernel/cpufeature.c              |   18 +-
 arch/arm64/kernel/mpam.c                    |   55 +
 arch/arm64/kernel/process.c                 |    7 +
 arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h  |   16 +
 arch/arm64/kvm/hyp/nvhe/switch.c            |   12 +
 arch/arm64/kvm/hyp/vhe/sysreg-sr.c          |    1 +
 drivers/resctrl/Kconfig                     |    9 +-
 drivers/resctrl/Makefile                    |    1 +
 drivers/resctrl/mpam_devices.c              |  298 ++-
 drivers/resctrl/mpam_internal.h             |  120 +-
 drivers/resctrl/mpam_resctrl.c              | 1926 +++++++++++++++++++
 drivers/resctrl/test_mpam_devices.c         |   66 +
 drivers/resctrl/test_mpam_resctrl.c         |  374 ++++
 include/linux/arm_mpam.h                    |   32 +
 21 files changed, 3038 insertions(+), 24 deletions(-)
 create mode 100644 arch/arm64/include/asm/mpam.h
 create mode 100644 arch/arm64/include/asm/resctrl.h
 create mode 100644 arch/arm64/kernel/mpam.c
 create mode 100644 drivers/resctrl/mpam_resctrl.c
 create mode 100644 drivers/resctrl/test_mpam_resctrl.c

-- 
2.39.5

Hi James and all,

As James is otherwise occupied, I am planning to post a follow up
version of this series once it's had time to be reviewed. I will be
posting my own review comments; please give them extra scrutiny.

On 12/5/25 21:58, James Morse wrote:
> This is the missing piece to make MPAM usable resctrl in user-space. This has
> shed its debugfs code and the read/write 'event configuration' for the monitors
> to make the series smaller.
> 
[...]
> 
> This series is based on arm64/for-next/core, and can be retrieved from:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/glue/rfc
> 
> There is no snapshot branch - this is it!
> I'll push the extras branch once I've gotten a handle on the DT shaped mess in
> there.

One major departure from the previous snapshot branches referenced in
the base driver series is that the same MPAM setting are used for
kernel-space and user-space. That is, MPAM1_EL1 is set to the same value
as MPAM0_EL1 rather than keeping the default value. The advantages of
this are that it is closer to the x86 model where the closid is globally
applicable, all partids are usable from user-space and user-space can't
bypass MPAM controls by doing the work in the kernel. However, this
causes some priority inversion where a high priority task waits to take
a mutex held by another whose resources are restricted by MPAM.
Thanks,

Ben

Hi Ben,

On Tue, Dec 9, 2025 at 3:40 PM Ben Horgan <ben.horgan@arm.com> wrote:
>
> Hi James and all,
>
> As James is otherwise occupied, I am planning to post a follow up
> version of this series once it's had time to be reviewed. I will be
> posting my own review comments; please give them extra scrutiny.
>
> On 12/5/25 21:58, James Morse wrote:
> > This is the missing piece to make MPAM usable resctrl in user-space. This has
> > shed its debugfs code and the read/write 'event configuration' for the monitors
> > to make the series smaller.
> >
> [...]
> >
> > This series is based on arm64/for-next/core, and can be retrieved from:
> > https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/glue/rfc
> >
> > There is no snapshot branch - this is it!
> > I'll push the extras branch once I've gotten a handle on the DT shaped mess in
> > there.
>
> One major departure from the previous snapshot branches referenced in
> the base driver series is that the same MPAM setting are used for
> kernel-space and user-space. That is, MPAM1_EL1 is set to the same value
> as MPAM0_EL1 rather than keeping the default value. The advantages of
> this are that it is closer to the x86 model where the closid is globally
> applicable, all partids are usable from user-space and user-space can't
> bypass MPAM controls by doing the work in the kernel. However, this
> causes some priority inversion where a high priority task waits to take
> a mutex held by another whose resources are restricted by MPAM.
> Thanks,

In our experience, the disadvantages of the x86 model were worse
because they triggered on hosts unintentionally, while making the
kernel do work unrestricted on behalf of the user at least requires
intentional abuse.

-Peter

Hi Peter,

On 12/9/25 15:53, Peter Newman wrote:
> Hi Ben,
> 
> On Tue, Dec 9, 2025 at 3:40 PM Ben Horgan <ben.horgan@arm.com> wrote:
>>
>> Hi James and all,
[...]
>>
>> One major departure from the previous snapshot branches referenced in
>> the base driver series is that the same MPAM setting are used for
>> kernel-space and user-space. That is, MPAM1_EL1 is set to the same value
>> as MPAM0_EL1 rather than keeping the default value. The advantages of
>> this are that it is closer to the x86 model where the closid is globally
>> applicable, all partids are usable from user-space and user-space can't
>> bypass MPAM controls by doing the work in the kernel. However, this
>> causes some priority inversion where a high priority task waits to take
>> a mutex held by another whose resources are restricted by MPAM.
>> Thanks,
> 
> In our experience, the disadvantages of the x86 model were worse
> because they triggered on hosts unintentionally, while making the
> kernel do work unrestricted on behalf of the user at least requires
> intentional abuse.
> 
> -Peter

Thanks for the quick feedback. Do you have any more data/information on
this that you can share?

Thanks,

Ben