x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid

MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be used
for different control groups.

This means once a CLOSID is allocated, all its monitoring ids may still be
dirty, and held in limbo.

Instead of allocating the first free CLOSID, on architectures where
CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID is enabled, search
closid_num_dirty_rmid[] to find the cleanest CLOSID.

The CLOSID found is returned to closid_alloc() for the free list
to be updated.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
Link: https://lore.kernel.org/r/20240213184438.16675-11-james.morse@arm.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>

1 files changed, 45 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 13b0c8d14f3d..101f1b112d17 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -386,6 +386,51 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
 	return ERR_PTR(-ENOSPC);
 }
 
+/**
+ * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
+ *                                  RMID are clean, or the CLOSID that has
+ *                                  the most clean RMID.
+ *
+ * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
+ * may not be able to allocate clean RMID. To avoid this the allocator will
+ * choose the CLOSID with the most clean RMID.
+ *
+ * When the CLOSID and RMID are independent numbers, the first free CLOSID will
+ * be returned.
+ */
+int resctrl_find_cleanest_closid(void)
+{
+	u32 cleanest_closid = ~0;
+	int i = 0;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+		return -EIO;
+
+	for (i = 0; i < closids_supported(); i++) {
+		int num_dirty;
+
+		if (closid_allocated(i))
+			continue;
+
+		num_dirty = closid_num_dirty_rmid[i];
+		if (num_dirty == 0)
+			return i;
+
+		if (cleanest_closid == ~0)
+			cleanest_closid = i;
+
+		if (num_dirty < closid_num_dirty_rmid[cleanest_closid])
+			cleanest_closid = i;
+	}
+
+	if (cleanest_closid == ~0)
+		return -ENOSPC;
+
+	return cleanest_closid;
+}
+
 /*
  * For MPAM the RMID value is not unique, and has to be considered with
  * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which