Hi Shaopeng,

On 09/09/2025 08:30, Shaopeng Tan (Fujitsu) wrote:

quoted

An MSC is a container of resources, each identified by their RIS index.
Some RIS are described by firmware to provide their position in the system.
Others are discovered when the driver probes the hardware.

To configure a resource it needs to be found by its class, e.g. 'L2'.
There are two kinds of grouping, a class is a set of components, which are
visible to user-space as there are likely to be multiple instances of the L2 cache.
(e.g. one per cluster or package)

struct mpam_components are a set of struct mpam_vmsc. A vMSC groups the
RIS in an MSC that control the same logical piece of hardware. (e.g. L2).
This is to allow hardware implementations where two controls are presented as
different RIS. Re-combining these RIS allows their feature bits to be or-ed. This
structure is not visible outside mpam_devices.c

struct mpam_vmsc are then a set of struct mpam_msc_ris, which are not
visible as each L2 cache may be composed of individual slices which need to
be configured the same as the hardware is not able to distribute the
configuration.

Add support for creating and destroying these structures.

A gfp is passed as the structures may need creating when a new RIS entry is
discovered when probing the MSC.

quoted

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 71a1fb1a9c75..5baf2a8786fb 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c

@@ -35,11 +34,483 @@

quoted

+static struct mpam_vmsc *mpam_vmsc_get(struct mpam_component
*comp,
+				       struct mpam_msc *msc, bool alloc,
+				       gfp_t gfp)
+{
+	struct mpam_vmsc *vmsc;
+
+	lockdep_assert_held(&mpam_list_lock);
+
+	list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
+		if (vmsc->msc->id == msc->id)
+			return vmsc;
+	}
+
+	if (!alloc)
+		return ERR_PTR(-ENOENT);

It seems like it is always false here.
If necessary, why not do this at the beginning of the function?

Because the VMSC may exist - in which case the 'get' function should return it
regardless of whether the caller wants to allocate it if its missing.

I'd anticipated callers like resctrl would want to grab components by things like cache-
id, without allocating them by accident. But that coded ended up just searching the lists
instead. I'll rip this out.


Thanks,

James