Re: [PATCH v2 17/29] arm_mpam: Extend reset logic to allow devices to be reset any time

Jonathan Cameron
2025-09-12T12:02:22Z

On Wed, 10 Sep 2025 20:42:57 +0000
James Morse <james.morse@arm.com> wrote:

> cpuhp callbacks aren't the only time the MSC configuration may need to
> be reset. Resctrl has an API call to reset a class.
> If an MPAM error interrupt arrives it indicates the driver has
> misprogrammed an MSC. The safest thing to do is reset all the MSCs
> and disable MPAM.
>
> Add a helper to reset RIS via their class. Call this from mpam_disable(),
> which can be scheduled from the error interrupt handler.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
> * more complete use of _srcu helpers.
> * Use guard macro for srcu.

I'm not seeing a strong reason for doing this for the case here and not
for cases in earlier patches like in mpam_cpu_online() I'm a fan of using
these broadly in a given code base, so would guard(srcu) in those earlier patches
as well.

Anyhow, one other trivial thing inline that you can ignore or not as you wish.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

> * Dropped a might_sleep() - something else will bark.
> ---
> drivers/resctrl/mpam_devices.c | 56 ++++++++++++++++++++++++++++++++--
> 1 file changed, 54 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index e7faf453b5d7..a9d3c4b09976 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -842,8 +842,6 @@ static int mpam_reset_ris(void *arg)
> u16 partid, partid_max;
> struct mpam_msc_ris *ris = arg;
>
> - mpam_assert_srcu_read_lock_held();
> -
> if (ris->in_reset_state)
> return 0;
>
> @@ -1340,8 +1338,56 @@ static void mpam_enable_once(void)
> mpam_partid_max + 1, mpam_pmg_max + 1);
> }
>
> +static void mpam_reset_component_locked(struct mpam_component *comp)
> +{
> + struct mpam_msc *msc;
> + struct mpam_vmsc *vmsc;
> + struct mpam_msc_ris *ris;
> +
> + lockdep_assert_cpus_held();
> +
> + guard(srcu)(&mpam_srcu);
> + list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
> + srcu_read_lock_held(&mpam_srcu)) {
> + msc = vmsc->msc;

Might be worth reducing scope of msc and ris

> +
> + list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
> + srcu_read_lock_held(&mpam_srcu)) {
> + if (!ris->in_reset_state)
> + mpam_touch_msc(msc, mpam_reset_ris, ris);
> + ris->in_reset_state = true;
> + }
> + }
> +}