wireguard-linux/drivers/resctrl/mpam_internal.h, branch stable

arm_mpam: Quirk CMN-650's CSU NRDY behaviour

2026-03-27T15:32:42Z

CMN-650 is afflicted with an erratum where the CSU NRDY bit never clears. This tells us the monitor never finishes scanning the cache. The erratum document says to wait the maximum time, then ignore the field. Add a flag to indicate whether this is the final attempt to read the counter, and when this quirk is applied, ignore the NRDY field. This means accesses to this counter will always retry, even if the counter was previously programmed to the same values. The counter value is not expected to be stable, it drifts up and down with each allocation and eviction. The CSU register provides the value for a point in time. Tested-by: Punit Agrawal Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Gavin Shan Co-developed-by: Ben Horgan Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: Add workaround for T241-MPAM-6

2026-03-27T15:32:41Z

The registers MSMON_MBWU_L and MSMON_MBWU return the number of requests rather than the number of bytes transferred. Bandwidth resource monitoring is performed at the last level cache, where each request arrive in 64Byte granularity. The current implementation returns the number of transactions received at the last level cache but does not provide the value in bytes. Scaling by 64 gives an accurate byte count to match the MPAM specification for the MSMON_MBWU and MSMON_MBWU_L registers. This patch fixes the issue by reporting the actual number of bytes instead of the number of transactions from __ris_msmon_read(). Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Punit Agrawal Tested-by: Peter Newman Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Gavin Shan Signed-off-by: Shanker Donthineni Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: Add workaround for T241-MPAM-4

2026-03-27T15:32:41Z

In the T241 implementation of memory-bandwidth partitioning, in the absence of contention for bandwidth, the minimum bandwidth setting can affect the amount of achieved bandwidth. Specifically, the achieved bandwidth in the absence of contention can settle to any value between the values of MPAMCFG_MBW_MIN and MPAMCFG_MBW_MAX. Also, if MPAMCFG_MBW_MIN is set zero (below 0.78125%), once a core enters a throttled state, it will never leave that state. The first issue is not a concern if the MPAM software allows to program MPAMCFG_MBW_MIN through the sysfs interface. This patch ensures program MBW_MIN=1 (0.78125%) whenever MPAMCFG_MBW_MIN=0 is programmed. In the scenario where the resctrl doesn't support the MBW_MIN interface via sysfs, to achieve bandwidth closer to MBW_MAX in the absence of contention, software should configure a relatively narrow gap between MBW_MIN and MBW_MAX. The recommendation is to use a 5% gap to mitigate the problem. Clear the feature MBW_MIN feature from the class to ensure we don't accidentally change behaviour when resctrl adds support for a MBW_MIN interface. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Fenghua Yu Reviewed-by: Gavin Shan Signed-off-by: Shanker Donthineni Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: Add workaround for T241-MPAM-1

2026-03-27T15:32:41Z

The MPAM bandwidth partitioning controls will not be correctly configured, and hardware will retain default configuration register values, meaning generally that bandwidth will remain unprovisioned. To address the issue, follow the below steps after updating the MBW_MIN and/or MBW_MAX registers. - Perform 64b reads from all 12 bridge MPAM shadow registers at offsets (0x360048 + slice*0x10000 + partid*8). These registers are read-only. - Continue iterating until all 12 shadow register values match in a loop. pr_warn_once if the values fail to match within the loop count 1000. - Perform 64b writes with the value 0x0 to the two spare registers at offsets 0x1b0000 and 0x1c0000. In the hardware, writes to the MPAMCFG_MBW_MAX MPAMCFG_MBW_MIN registers are transformed into broadcast writes to the 12 shadow registers. The final two writes to the spare registers cause a final rank of downstream micro-architectural MPAM registers to be updated from the shadow copies. The intervening loop to read the 12 shadow registers helps avoid a race condition where writes to the spare registers occur before all shadow registers have been updated. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Punit Agrawal Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Gavin Shan Signed-off-by: Shanker Donthineni Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: Add quirk framework

2026-03-27T15:32:27Z

The MPAM specification includes the MPAMF_IIDR, which serves to uniquely identify the MSC implementation through a combination of implementer details, product ID, variant, and revision. Certain hardware issues/errata can be resolved using software workarounds. Introduce a quirk framework to allow workarounds to be enabled based on the MPAMF_IIDR value. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Zeng Heng Tested-by: Punit Agrawal Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Jonathan Cameron Reviewed-by: Gavin Shan Signed-off-by: Shanker Donthineni Co-developed-by: Ben Horgan Signed-off-by: Ben Horgan Co-developed-by: James Morse Signed-off-by: James Morse

arm_mpam: resctrl: Call resctrl_init() on platforms that can support resctrl

2026-03-27T15:32:19Z

Now that MPAM links against resctrl, call resctrl_init() to register the filesystem and setup resctrl's structures. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Peter Newman Tested-by: Zeng Heng Tested-by: Punit Agrawal Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Jonathan Cameron Reviewed-by: Gavin Shan Co-developed-by: Ben Horgan Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: resctrl: Allow resctrl to allocate monitors

2026-03-27T15:31:38Z

When resctrl wants to read a domain's 'QOS_L3_OCCUP', it needs to allocate a monitor on the corresponding resource. Monitors are allocated by class instead of component. Add helpers to allocate a CSU monitor. These helper return an out of range value for MBM counters. Allocating a montitor context is expected to block until hardware resources become available. This only makes sense for QOS_L3_OCCUP as unallocated MBM counters are losing data. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Peter Newman Tested-by: Zeng Heng Tested-by: Punit Agrawal Tested-by: Jesse Chick Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Jonathan Cameron Reviewed-by: Gavin Shan Co-developed-by: Ben Horgan Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: resctrl: Add monitor initialisation and domain boilerplate

2026-03-27T15:31:10Z

Add the boilerplate that tells resctrl about the mpam monitors that are available. resctrl expects all (non-telemetry) monitors to be on the L3 and so advertise them there and invent an L3 resctrl resource if required. The L3 cache itself has to exist as the cache ids are used as the domain ids. Bring the resctrl monitor domains online and offline based on the cpus they contain. Support for specific monitor types is left to later. Tested-by: Punit Agrawal Reviewed-by: Zeng Heng Reviewed-by: Jonathan Cameron Signed-off-by: Ben Horgan Reviewed-by: Gavin Shan Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Jesse Chick Signed-off-by: James Morse

arm_mpam: resctrl: Add CDP emulation

2026-03-27T15:30:10Z

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. Also, update these per-cpu values and sync the resulting mpam partid/pmg configuration to hardware. resctrl can enable CDP for L2 caches, L3 caches or both. When it is enabled by one and not the other MPAM globally enabled CDP but hides the effect on the other cache resource. This hiding is possible as CPOR is the only supported cache control and that uses a resource bitmap; two partids with the same bitmap act as one. Awkwardly, the MB controls don't implement CDP and CDP can't be hidden as the memory bandwidth control is a maximum per partid which can't be modelled with more partids. If the total maximum is used for both the data and instruction partids then then the maximum may be exceeded and if it is split in two then the one using more bandwidth will hit a lower limit. Hence, hide the MB controls completely if CDP is enabled for any resource. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Peter Newman Tested-by: Zeng Heng Tested-by: Punit Agrawal Tested-by: Jesse Chick Cc: Dave Martin Cc: Amit Singh Tomar Reviewed-by: Zeng Heng Reviewed-by: Shaopeng Tan Reviewed-by: Jonathan Cameron Reviewed-by: Gavin Shan Co-developed-by: Ben Horgan Signed-off-by: Ben Horgan Signed-off-by: James Morse

arm_mpam: resctrl: Implement resctrl_arch_reset_all_ctrls()

2026-03-27T15:29:42Z

We already have a helper for resetting an mpam class and component. Hook it up to resctrl_arch_reset_all_ctrls() and the domain offline path. Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Peter Newman Tested-by: Zeng Heng Tested-by: Punit Agrawal Tested-by: Jesse Chick Reviewed-by: Shaopeng Tan Reviewed-by: Zeng Heng Reviewed-by: Jonathan Cameron Reviewed-by: Gavin Shan Co-developed-by: Ben Horgan Signed-off-by: Ben Horgan Signed-off-by: James Morse