x86/resctrl: Expand the width of domid by replacing mon_data_bits

MPAM platforms retrieve the cache-id property from the ACPI PPTT table.
The cache-id field is 32 bits wide. Under resctrl, the cache-id becomes
the domain-id, and is packed into the mon_data_bits union bitfield.
The width of cache-id in this field is 14 bits.

Expanding the union would break 32bit x86 platforms as this union is
stored as the kernfs kn->priv pointer. This saved allocating memory
for the priv data storage.

The firmware on MPAM platforms have used the PPTT cache-id field to
expose the interconnect's id for the cache, which is sparse and uses
more than 14 bits. Use of this id is to enable PCIe direct cache
injection hints. Using this feature with VFIO means the value provided
by the ACPI table should be exposed to user-space.

To support cache-id values greater than 14 bits, convert the
mon_data_bits union to a structure. These are shared between control
and monitor groups, and are allocated on first use. The list of
allocated struct mon_data is free'd when the filesystem is umount()ed.

Co-developed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/20250515165855.31452-13-james.morse@arm.com

1 files changed, 19 insertions, 20 deletions

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 576383a808a2..01cb0ff89c85 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -89,27 +89,26 @@ struct mon_evt {
 };
 
 /**
- * union mon_data_bits - Monitoring details for each event file.
- * @priv:              Used to store monitoring event data in @u
- *                     as kernfs private data.
- * @u.rid:             Resource id associated with the event file.
- * @u.evtid:           Event id associated with the event file.
- * @u.sum:             Set when event must be summed across multiple
- *                     domains.
- * @u.domid:           When @u.sum is zero this is the domain to which
- *                     the event file belongs. When @sum is one this
- *                     is the id of the L3 cache that all domains to be
- *                     summed share.
- * @u:                 Name of the bit fields struct.
+ * struct mon_data - Monitoring details for each event file.
+ * @list:            Member of the global @mon_data_kn_priv_list list.
+ * @rid:             Resource id associated with the event file.
+ * @evtid:           Event id associated with the event file.
+ * @sum:             Set when event must be summed across multiple
+ *                   domains.
+ * @domid:           When @sum is zero this is the domain to which
+ *                   the event file belongs. When @sum is one this
+ *                   is the id of the L3 cache that all domains to be
+ *                   summed share.
+ *
+ * Pointed to by the kernfs kn->priv field of monitoring event files.
+ * Readers and writers must hold rdtgroup_mutex.
  */
-union mon_data_bits {
-	void *priv;
-	struct {
-		unsigned int rid		: 10;
-		enum resctrl_event_id evtid	: 7;
-		unsigned int sum		: 1;
-		unsigned int domid		: 14;
-	} u;
+struct mon_data {
+	struct list_head	list;
+	enum resctrl_res_level	rid;
+	enum resctrl_event_id	evtid;
+	int			domid;
+	bool			sum;
 };
 
 /**