[PATCH v2 09/16] x86,fs/resctrl: Add the functionality to configure PLZA

Babu Moger
2026-03-12T20:38:39Z

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@amd.com>
---
v2: - Updated the commit message to include the sequence of steps to enable PLZA.
Added mode code comments for clarity.
Added kmode to functin names to be generic.
---
arch/x86/include/asm/resctrl.h | 19 ++++++
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 77 +++++++++++++++++++++++
include/linux/resctrl.h | 30 +++++++++
3 files changed, 126 insertions(+)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index e0a992abaeb4..167be18983c1 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -186,6 +186,25 @@ static inline bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 ignored,
return READ_ONCE(tsk->rmid) == rmid;
}

+/**
+ * resctrl_arch_set_cpu_kmode() - Set per-CPU kernel mode state for PLZA programming
+ * @cpu: Logical CPU to update.
+ * @closid: CLOSID to use for kernel work on this CPU when kmode is enabled.
+ * @rmid: RMID to use for kernel work on this CPU when kmode is enabled.
+ * @enable: 1 to enable PLZA on this CPU; 0 to leave disabled. Stored in default_kmode.
+ *
+ * Stores the given CLOSID, RMID, and enable value in per-CPU state (kmode_closid,
+ * kmode_rmid, default_kmode). The actual MSR_IA32_PQR_PLZA_ASSOC write is done
+ * separately (e.g. via on_each_cpu_mask) so that closid/rmid are set on all CPUs
+ * in the domain before PLZA_EN is set, per the PLZA programming sequence.
+ */
+static inline void resctrl_arch_set_cpu_kmode(int cpu, u32 closid, u32 rmid, u32 enable)
+{
+ WRITE_ONCE(per_cpu(pqr_state.default_kmode, cpu), enable);
+ WRITE_ONCE(per_cpu(pqr_state.kmode_closid, cpu), closid);
+ WRITE_ONCE(per_cpu(pqr_state.kmode_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..b5dfe30aca26 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -131,3 +131,80 @@ int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable)

return 0;
}
+
+/*
+ * IPI callback: write MSR_IA32_PQR_PLZA_ASSOC on this CPU (AMD PLZA).
+ */
+static void resctrl_kmode_set_one_amd(void *arg)
+{
+ union qos_pqr_plza_assoc *plza = arg;
+
+ wrmsrl(MSR_IA32_PQR_PLZA_ASSOC, plza->full);
+}
+
+/**
+ * resctrl_arch_configure_kmode() - x86/AMD: program PLZA per control domain
+ *
+ * For each control domain, first sets per-CPU state (closid, rmid, enable=0)
+ * on all CPUs in the domain, then writes MSR_IA32_PQR_PLZA_ASSOC on each CPU
+ * so that closid/closid_en (and optionally rmid/rmid_en) are programmed
+ * before PLZA_EN is set, per the PLZA programming sequence.
+ */
+void resctrl_arch_configure_kmode(struct rdt_resource *r, struct resctrl_kmode_cfg *kcfg,
+ u32 closid, u32 rmid)
+{
+ union qos_pqr_plza_assoc plza = { 0 };
+ struct rdt_ctrl_domain *d;
+ int cpu;
+
+ if (kcfg->kmode_cur & INHERIT_CTRL_AND_MON)
+ return;
+
+ if (kcfg->kmode_cur & GLOBAL_ASSIGN_CTRL_ASSIGN_MON) {
+ 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_kmode(cpu, closid, rmid, 0);
+ on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_kmode_set_one_amd, &plza, 1);
+ }
+}
+
+/**
+ * resctrl_arch_set_kmode() - x86/AMD: set PLZA enable/disable on a set of CPUs
+ * @cpu_mask: CPUs to update (e.g. a control domain's cpu_mask).
+ * @kcfg: Current kernel mode configuration.
+ * @closid: CLOSID to use for kernel work when a global assign mode is active.
+ * @rmid: RMID to use for kernel work when GLOBAL_ASSIGN_CTRL_ASSIGN_MON is active.
+ * @enable: True to set MSR_IA32_PQR_PLZA_ASSOC.PLZA_EN; false to clear it.
+ *
+ * Writes MSR_IA32_PQR_PLZA_ASSOC on each CPU in @cpu_mask (via IPI) and updates
+ * per-CPU state. No-op when kmode_cur is INHERIT_CTRL_AND_MON. Call after
+ * resctrl_arch_configure_kmode() so that closid/rmid are programmed before
+ * PLZA_EN is set.
+ */
+void resctrl_arch_set_kmode(cpumask_var_t cpu_mask, struct resctrl_kmode_cfg *kcfg,
+ u32 closid, u32 rmid, bool enable)
+{
+ int cpu;
+ union qos_pqr_plza_assoc plza = { 0 };
+
+ if (kcfg->kmode_cur & INHERIT_CTRL_AND_MON)
+ return;
+
+ if (kcfg->kmode_cur & GLOBAL_ASSIGN_CTRL_ASSIGN_MON) {
+ plza.split.rmid = rmid;
+ plza.split.rmid_en = 1;
+ }
+ plza.split.closid = closid;
+ plza.split.closid_en = 1;
+ plza.split.plza_en = enable;
+
+ on_each_cpu_mask(cpu_mask, resctrl_kmode_set_one_amd, &plza, 1);
+ for_each_cpu(cpu, cpu_mask)
+ resctrl_arch_set_cpu_kmode(cpu, closid, rmid, enable);
+}
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 2c36d1ac392f..3f3e8c1e549b 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -709,6 +709,36 @@ bool resctrl_arch_get_io_alloc_enabled(struct rdt_resource *r);
*/
void resctrl_arch_get_kmode_cfg(struct resctrl_kmode_cfg *kcfg);

+/**
+ * resctrl_arch_configure_kmode() - Program kernel mode (e.g. PLZA) for all domains
+ * @r: The resctrl resource (scope for control domains).
+ * @kcfg: Current kernel mode configuration.
+ * @closid: CLOSID to use for kernel work when a global assign mode is active.
+ * @rmid: RMID to use for kernel work when GLOBAL_ASSIGN_CTRL_ASSIGN_MON is active.
+ *
+ * Programs each control domain so that kernel work uses the given CLOSID/RMID
+ * per the active kernel mode (e.g. MSR_IA32_PQR_PLZA_ASSOC on x86). No-op when
+ * kmode_cur is INHERIT_CTRL_AND_MON. May be called from any CPU.
+ */
+void resctrl_arch_configure_kmode(struct rdt_resource *r, struct resctrl_kmode_cfg *kcfg,
+ u32 closid, u32 rmid);
+
+/**
+ * resctrl_arch_set_kmode() - Set kernel mode (e.g. PLZA) on a set of CPUs
+ * @cpu_mask: CPUs to update (e.g. a control domain's cpu_mask).
+ * @kcfg: Current kernel mode configuration.
+ * @closid: CLOSID to use for kernel work when a global assign mode is active.
+ * @rmid: RMID to use for kernel work when GLOBAL_ASSIGN_CTRL_ASSIGN_MON is active.
+ * @enable: True to set MSR_IA32_PQR_PLZA_ASSOC.PLZA_EN on the CPUs; false to clear it.
+ *
+ * Writes MSR_IA32_PQR_PLZA_ASSOC on each CPU in @cpu_mask and updates per-CPU
+ * state. No-op when kmode_cur is INHERIT_CTRL_AND_MON. Call after
+ * resctrl_arch_configure_kmode() so that closid/rmid are programmed before
+ * PLZA_EN is set. May be called from any CPU.
+ */
+void resctrl_arch_set_kmode(cpumask_var_t cpu_mask, struct resctrl_kmode_cfg *kcfg,
+ u32 closid, u32 rmid, bool enable);
+
extern unsigned int resctrl_rmid_realloc_threshold;
extern unsigned int resctrl_rmid_realloc_limit;

--
2.43.0