Re: [PATCH v3 05/12] x86/resctrl: Initialize supported kernel modes for PLZA

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

Hi Reinette,

On 6/16/26 18:35, Reinette Chatre wrote:
> Hi Babu,
> 
> On 4/30/26 4:24 PM, Babu Moger wrote:
>> Resctrl subsystem tracks which kernel-mode CLOSID/RMID policies the
>> platform can offer via struct resctrl_kmode_cfg and
>> resctrl_arch_get_kmode_support(). AMD PLZA (Privilege Level Zero
>> Association) is the x86 feature that allows kernel traffic to use an
>> assigned CLOSID alone or CLOSID and RMID together.
>>
>> Report the available kernel-modes when x86 PLZA is enabled.
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>> v3: New patch to report all the supported kernel mode by arch.
>> ---
>>   arch/x86/kernel/cpu/resctrl/core.c | 15 +++++++++++++++
>>   1 file changed, 15 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>> index 4a8717157e3e..699d8bb82875 100644
>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>> @@ -894,6 +894,21 @@ bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt)
>>   	}
>>   }
>>   
>> +/**
>> + * resctrl_arch_get_kmode_support() - x86: record which kernel-mode policies hardware supports
>> + * @kcfg:	Cumulative snapshot; OR bits into @kcfg->kmode (see &struct resctrl_kmode_cfg).
> 
> If this is intended to be a cumulative snapshot this is a very subtle requirement
> for architectures to "do the right thing" here. To make this more robust I think it will be
> simpler if resctrl fs boots with resctrl_kcfg initialized to expected defaults.
> Instead of this callback resctrl can add resctrl_set_kmode_support(u32 kmodes)
> that the architecture *may* use to further initialize the kmodes supported by it. This
> function is implemented by resctrl fs, instead of architecture, and it can fail if
> architecture does not support INHERIT_CTRL_AND_MON. This will help to keep
> struct resctrl_kmode_cfg private to resctrl fs while enforcing any assumptions about
> which modes are required to be supported.

Yes, agreed. I will move resctrl_set_kmode_support() to the FS layer and 
have the architecture code invoke it when setting the kmodes.

That will make the struct resctrl_kmode_cfg private to FS layer.

Thanks
Babu