linux-kernel - [RFC PATCH 14/19] x86,fs/resctrl: Add the functionality to configure PLZA

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Message-ID: <84b6ec2a2b41647f44d6138bc5e13ceab3aa3589.1769029977.git.babu.moger@amd.com>
Date: Wed, 21 Jan 2026 15:12:52 -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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	<dave.hansen@...ux.intel.com>
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Subject: [RFC PATCH 14/19] x86,fs/resctrl: Add the functionality to configure PLZA

Privilege Level Zero Association (PLZA) is configured by writing to
MSR_IA32_PQR_PLZA_ASSOC. PLZA is disabled by default on all logical
processors in the QOS Domain. System software must follow the following
sequence.

1. Set the closid, closid_en, rmid and rmid_en fields of
MSR_IA32_PQR_PLZA_ASSOC to the desired configuration on all logical
processors in the QOS Domain.

2. Set MSR_IA32_PQR_PLZA_ASSOC[PLZA_EN]=1 for
all logical processors in the QOS domain where PLZA should be enabled.

MSR_IA32_PQR_PLZA_ASSOC[PLZA_EN] may have a different value on every
logical processor in the QOS domain. The system software should perform
this as a read-modify-write to avoid changing the value of closid_en,
closid, rmid_en, and rmid fields of MSR_IA32_PQR_PLZA_ASSOC.

Signed-off-by: Babu Moger <babu.moger@....com>
---
 arch/x86/include/asm/resctrl.h            |  7 +++++++
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 25 +++++++++++++++++++++++
 include/linux/resctrl.h                   | 11 ++++++++++
 3 files changed, 43 insertions(+)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 76de7d6051b7..89b38948be1a 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -193,6 +193,13 @@ static inline bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 ignored,
 	return READ_ONCE(tsk->rmid) == rmid;
 }
 
+static inline void resctrl_arch_set_cpu_plza(int cpu, u32 closid, u32 rmid, u32 enable)
+{
+	WRITE_ONCE(per_cpu(pqr_state.default_plza, cpu), enable);
+	WRITE_ONCE(per_cpu(pqr_state.plza_closid, cpu), closid);
+	WRITE_ONCE(per_cpu(pqr_state.plza_rmid, cpu), rmid);
+}
+
 static inline void resctrl_arch_sched_in(struct task_struct *tsk)
 {
 	if (static_branch_likely(&rdt_enable_key))
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index b20e705606b8..79ed41bde810 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -131,3 +131,28 @@ int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable)
 
 	return 0;
 }
+
+static void resctrl_plza_set_one_amd(void *arg)
+{
+	union qos_pqr_plza_assoc *plza = arg;
+
+	wrmsrl(MSR_IA32_PQR_PLZA_ASSOC, plza->full);
+}
+
+void resctrl_arch_plza_setup(struct rdt_resource *r, u32 closid, u32 rmid)
+{
+	union qos_pqr_plza_assoc plza = { 0 };
+	struct rdt_ctrl_domain *d;
+	int cpu;
+
+	plza.split.rmid = rmid;
+	plza.split.rmid_en = 1;
+	plza.split.closid = closid;
+	plza.split.closid_en = 1;
+
+	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+		for_each_cpu(cpu, &d->hdr.cpu_mask)
+			resctrl_arch_set_cpu_plza(cpu, closid, rmid, 0);
+		on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_plza_set_one_amd, &plza, 1);
+	}
+}
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index ae252a0e6d92..ef26253ad24a 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -704,6 +704,17 @@ int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable);
  */
 bool resctrl_arch_get_io_alloc_enabled(struct rdt_resource *r);
 
+/*
+ * resctrl_arch_plza_setup() - Reset all private state associated with
+ *				   all rmids and eventids.
+ * @r:		The resctrl resource.
+ * @closid:	The CLOSID to be configered for PLZA.
+ * @rmid:	The RMID to be configered for PLZA.
+ *
+ * This can be called from any CPU.
+ */
+void resctrl_arch_plza_setup(struct rdt_resource *r, u32 closid, u32 rmid);
+
 extern unsigned int resctrl_rmid_realloc_threshold;
 extern unsigned int resctrl_rmid_realloc_limit;
 
-- 
2.34.1