Re: [PATCH v6 00/10] arm_mpam: Add MPAM-Fb firmware support

[Andre Przywara <andre.przywara@arm.com>]

Hi Ben,

On 7/30/26 19:10, Ben Horgan wrote:
> Hi Andre,
> 
> On 7/30/26 16:25, Andre Przywara wrote:
> [...]
>> The first six patches rework all MSC access wrappers to propagate error
>> information. Pure MMIO based MSC accesses would never fail, but the
>> MPAM-Fb access can go wrong in multiple ways. The patches have been split
>> up purely for reviewing reasons, if the number is a problem, we could as
>> well squash them. Please note that until the very last patch of this series
>> any MSC accesses would always only return 0, it's only the final enablement
>> of MPAM-Fb that could possibly introduce errors. Hence all former patches
>> can add error handling gradually, those code paths wouldn't be triggered
>> before patch 10/10.
> 
> I had a go at injecting some errors and noticed that at least some aren't getting to user space.
> When writing the schemata file any MPAM-Fb error is not propagated to the user. The
> resctrl_arch_update_domains() continues to return 0 as there are some missing links in the chain
> down to the writes, e.g. __write_config() always returns 0.

Ah yeah, that's true. With the write functions using a compatible 
prototype (just ignoring the new return value) this is harder to check, 
since the compiler is just fine with it.

So I propagate all MSC access errors now in mpam_reprogram_ris_partid(), 
and the depending mpam_apply_config(), __write_config and 
mpam_reset_ris() functions. From my quick analysis I'd say that covers 
all functions now that mpam_devices.c exports. That will be a new patch 
07/11.

Cheers,
Andre