Hi Ben,

On 29/08/2025 15:30, Ben Horgan wrote:

On 8/22/25 16:30, James Morse wrote:

quoted

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.

quoted

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 759244966736..3516cbe8623e 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c

@@ -1569,6 +1567,66 @@ static void mpam_enable_once(void)

quoted

+/*
+ * Called in response to an error IRQ.
+ * All of MPAMs errors indicate a software bug, restore any modified
+ * controls to their reset values.
+ */
+void mpam_disable(void)
+{
+	int idx;
+	struct mpam_class *class;
+
+	idx = srcu_read_lock(&mpam_srcu);
+	list_for_each_entry_srcu(class, &mpam_classes, classes_list,
+				 srcu_read_lock_held(&mpam_srcu))

Why do you use list_for_each_entry_srcu() here when in other places you
use list_for_each_entry_rcu()?

It's a mistake. I was part way making this use RCU when someone 'invented' the
firmware interface meaning readl() needs to be able to sleep...
Those were added in a later patch than I thought, and I missed fixing them up.

I think the srcu version provides extra checking - and is the correct one to use.
I'll fix those -- thanks for spotting it!


Thanks,

James

quoted

+		mpam_reset_class(class);
+	srcu_read_unlock(&mpam_srcu, idx);
+}