linux-kernel - [RFC PATCH 10/19] fs/resctrl: Expose plza

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Message-ID: <bcf600adf9e632ae486f08fe857475167218f26c.1769029977.git.babu.moger@amd.com>
Date: Wed, 21 Jan 2026 15:12:48 -0600
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <tony.luck@...el.com>, <reinette.chatre@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <babu.moger@....com>,
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Subject: [RFC PATCH 10/19] fs/resctrl: Expose plza_capable via control info file

Add a new resctrl info file, plza_capable, to report whether a resource
supports the PLZA capability. Allows user to query PLZA support directly
through resctrl without having to infer it from other resource attributes.

Signed-off-by: Babu Moger <babu.moger@....com>
---
 Documentation/filesystems/resctrl.rst | 17 +++++++++++++++++
 fs/resctrl/rdtgroup.c                 | 17 +++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 3d66814a1d7f..1de55b5cb0e3 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -30,6 +30,7 @@ ABMC (Assignable Bandwidth Monitoring Counters)			""
 SDCIAE (Smart Data Cache Injection Allocation Enforcement)	""
 GMBA (Global Memory Bandwidth Allocation)                       ""
 GSMBA (Global Slow Memory Bandwidth Allocation)                 ""
+PLZA (Privilege Level Zero association)                         ""
 =============================================================== ================================
 
 Historically, new features were made visible by default in /proc/cpuinfo. This
@@ -151,6 +152,22 @@ related to allocation:
 			"1":
 			      Non-contiguous 1s value in CBM is supported.
 
+"plza_capable":
+                Indicates the availability of Privilege Level Zero Association (PLZA).
+                PLZA is a hardware feature that enables automatic association of execution
+                at Privilege Level Zero (CPL=0) with a designated Class of Service
+                Identifier (CLOSID) and/or Resource Monitoring Identifier (RMID).
+                This mechanism allows the system to override the default per-thread
+                association for threads operating at CPL=0 when necessary. Additionally,
+                PLZA provides configuration capabilities for defining a dedicated resource
+                control group and assigning CPUs and tasks to operate under CLOSID
+                constraints reserved exclusively for PLZA.
+
+			"1":
+                                Resource supports the feature.
+			"0":
+                                Support not available for this resource.
+
 "io_alloc":
 		"io_alloc" enables system software to configure the portion of
 		the cache allocated for I/O traffic. File may only exist if the
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index fc034f4481e3..d773bf77bcc6 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1260,6 +1260,16 @@ static ssize_t max_threshold_occ_write(struct kernfs_open_file *of,
 	return nbytes;
 }
 
+static int rdt_plza_show(struct kernfs_open_file *of, struct seq_file *seq, void *v)
+{
+	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
+	struct rdt_resource *r = s->res;
+
+	seq_printf(seq, "%d\n", r->plza_capable);
+
+	return 0;
+}
+
 /*
  * rdtgroup_mode_show - Display mode of this resource group
  */
@@ -1991,6 +2001,13 @@ static struct rftype res_common_files[] = {
 		.seq_show	= rdt_delay_linear_show,
 		.fflags		= RFTYPE_CTRL_INFO | RFTYPE_RES_MB,
 	},
+	{
+		.name		= "plza_capable",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdt_plza_show,
+		.fflags		= RFTYPE_CTRL_INFO,
+	},
 	/*
 	 * Platform specific which (if any) capabilities are provided by
 	 * thread_throttle_mode. Defer "fflags" initialization to platform
-- 
2.34.1