Re: [PATCH v3 00/12] x86/resctrl: Add kernel-mode (e.g., PLZA) support to the resctrl subsystem

[Babu Moger <babu.moger@amd.com>]

Hi Qinyun,

On 6/8/26 04:23, Qinyun Tan wrote:
> Hi Babu,
> 
> While reviewing this series I noticed two cross-architecture issues.
> 
> 1) aarch64 allyesconfig link failure
> 
>     resctrl_arch_configure_kmode() and resctrl_arch_get_kmode_support()
>     are declared in include/linux/resctrl.h:
> 
>       void resctrl_arch_get_kmode_support(struct resctrl_kmode_cfg *kcfg);
>       void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask,
>                                         u32 closid, u32 rmid, bool enable);
> 
>     but only implemented under arch/x86/.  ARM MPAM selects
>     CONFIG_RESCTRL_FS, so fs/resctrl/rdtgroup.c is compiled on aarch64
>     and the linker fails:
> 
>       ld: fs/resctrl/rdtgroup.o: in function `rdtgroup_config_kmode_clear':
>       rdtgroup.c: undefined reference to `resctrl_arch_configure_kmode'
>       ld: fs/resctrl/rdtgroup.o: in function `resctrl_init':
>       rdtgroup.c: undefined reference to `resctrl_arch_get_kmode_support'
> 
>     Other arch-specific functions already have empty stubs in
>     drivers/resctrl/mpam_resctrl.c, e.g.:
> 
>       int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable)
>       {
>               return -EOPNOTSUPP;
>       }
> 
>     Adding the same for the two kmode functions would fix the build.

Good catch. Will add in empty stubs in next revision for these 3 functions.

> 
> 2) info/kernel_mode visible on non-PLZA platforms
> 
>     The "kernel_mode" entry is registered with fflags = RFTYPE_TOP_INFO:
> 
>       {
>               .name           = "kernel_mode",
>               .mode           = 0644,
>               ...
>               .fflags         = RFTYPE_TOP_INFO,
>       },
> 
>     This makes the file appear unconditionally under info/ -- even on
>     platforms without PLZA (ARM MPAM, older AMD/Intel without
>     X86_FEATURE_PLZA).  On those platforms the file only shows the
>     default inherit_ctrl_and_mon mode, which is confusing since there
>     are no other modes to switch to.

This is expected. We intended to expose the info/kernel_mode file for 
all architectures, and it will display the default mode 
inherit_ctrl_and_mon.

This approach was also suggested by Reinette.
https://lore.kernel.org/lkml/2ab556af-095b-422b-9396-f845c6fd0342@intel.com/

Thanks
Babu