[RFC PATCH 8/8] fs/resctrl: Suppress creation of cbm_mask info file on asymmetric systems

[Tony Luck]

Hybrid CPUs with a mix of P-cores and E-cores may support different
cache allocation bit masks. The per-domain masks are described in the
info/L2A/schemata/L2A/max file.

The cbm_mask file contains a single value and cannot describe an
asymmetric system.

Skip creating cbm_mask in the info/L2A directory.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 Documentation/filesystems/resctrl.rst | 4 ++++
 fs/resctrl/internal.h                 | 2 ++
 fs/resctrl/rdtgroup.c                 | 5 ++++-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index de162280a0fe..25e9e5e5e738 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -91,6 +91,10 @@ related to allocation:
 "cbm_mask":
 		The bitmask which is valid for this resource.
 		This mask is equivalent to 100%.
+		Not present for asymmetric L2 allocation (L2A), where
+		valid masks can differ between domains. Use the bitmap
+		control's "max" file under "info/L2A/schemata/" to obtain
+		the per-domain masks.
 "min_cbm_bits":
 		The minimum number of consecutive bits which
 		must be set when writing a mask.
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 4bd09b1541c7..d93d349db08b 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -261,6 +261,8 @@ struct rdtgroup {
 
 #define RFTYPE_RES_PERF_PKG		BIT(12)
 
+#define RFTYPE_RES_COMMON_CBM		BIT(13)
+
 #define RFTYPE_CTRL_INFO		(RFTYPE_INFO | RFTYPE_CTRL)
 
 #define RFTYPE_MON_INFO			(RFTYPE_INFO | RFTYPE_MON)
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 46d39332706e..5cf6a257bea8 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -2196,7 +2196,8 @@ static struct rftype res_common_files[] = {
 		.mode		= 0444,
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= rdt_default_ctrl_show,
-		.fflags		= RFTYPE_CTRL_INFO | RFTYPE_RES_CACHE,
+		.fflags		= RFTYPE_CTRL_INFO | RFTYPE_RES_CACHE |
+				  RFTYPE_RES_COMMON_CBM,
 	},
 	{
 		.name		= "num_mbm_cntrs",
@@ -3024,6 +3025,8 @@ static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)
 	list_for_each_entry(f, &rdt_resource_final_all, list) {
 		r = f->res;
 		fflags = fflags_from_resource(r) | RFTYPE_CTRL_INFO;
+		if ((fflags & RFTYPE_RES_CACHE) && !r->asymmetric)
+			fflags |= RFTYPE_RES_COMMON_CBM;
 		kn_res = rdtgroup_mkdir_info_resdir(f, f->name, fflags);
 		if (IS_ERR(kn_res)) {
 			ret = PTR_ERR(kn_res);
-- 
2.56.0