Re: [PATCH] arm_mpam: Fix MPAM reset on resctrl unmount by clearing in_reset_state

[Zeng Heng]

Hi Ben,

On 2026/2/27 22:16, Ben Horgan wrote:
> On 2/17/26 15:59, Ben Horgan wrote:
> > Hi Zeng,
> >
> > On 2/13/26 07:50, Zeng Heng wrote:
> > > When resctrl is unmounted, MPAM components should be reset to default
> > > configurations to avoid impacting system performance. However, after
> > > a user updates MPAM configuration via mpam_apply_config(), the
> > > in_reset_state flag remains true, causing mpam_reset_ris() to skip
> > > the actual register restoration on subsequent resets.
> > >
> > > For example, after mounting resctrl and modifying the root group's
> > > schemata (e.g., changing MBMAX/MBMIN values), unmounting resctrl
> >
> > nit: MBMIN isn't currently supported in resctrl. I'd just drop the
> > part in brackets.
> >
> > > would leave the modified MPAM settings in hardware registers since
> > > mpam_reset_ris() returns early due to in_reset_state still being true.
> > > This results in persistent performance restrictions even after resctrl
> > > is umounted.
> > >
> > > Fix by clearing in_reset_state to false immediately after successful
> > > configuration application, ensuring that the next reset operation
> > > properly restores MPAM register defaults.
> > >
> > > Fixes: f188a36ca241 ("arm_mpam: Reset MSC controls from cpuhp callbacks")
> >
> > mpam_apply_config() doesn't exist in this commit. I would have expected:
> > Fixes: 09b89d2a72f3 ("arm_mpam: Allow configuration to be applied and restored during cpu online")
> >
> > > Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> >
> > The change and justification looks good to me.
> >
> > Acked-by: Ben Horgan <ben.horgan@xxxxxxx>
>
> I'll add this on to the start of the current mpam resctrl series as even
> though this is squashing an existing bug it can't be hit until mpam has
> a user interface and so doesn't need to go as a fix.
>
> Thanks,
>
> Ben
OK, get it.

Best regards,
Zeng Heng