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

[Babu Moger]

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@xxxxxxx>
> > ---
> > 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