[PATCH 2/4] resctrl: Fix PLZA RMID_EN to be mode-based and relax RDTMON_GROUP constraint for assign_mon
From: Qinyun Tan
Date: Thu Jun 11 2026 - 07:17:26 EST
Two issues identified during review of the upstream v3 PLZA patches,
confirmed by the patch author (Babu Moger):
1) resctrl_arch_configure_kmode() hardcodes rmid_en=1 for both
inherit_mon and assign_mon modes. Per the AMD hardware manual
(Publication #69193), RMID_EN is a source selector: when set,
CPL=0 uses the PLZA RMID; when clear, CPL=0 falls back to
PQR_ASSOC[RMID] (the user process's RMID). With rmid_en=1 in
inherit_mon mode, kernel-mode traffic is always counted under the
PLZA group's RMID, defeating the "inherit" semantics.
Add a bool assign_rmid parameter to resctrl_arch_configure_kmode().
Set rmid_en=1 only for assign_mon (GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU),
and rmid_en=0 for inherit_mon (GLOBAL_ASSIGN_CTRL_INHERIT_MON_PER_CPU)
so that kernel-mode RMID correctly inherits from PQR_ASSOC.
The assign_rmid value is derived from the active kmode in all three
call sites: rdtgroup_config_kmode(), rdtgroup_config_kmode_clear(),
and kmode_cpus_write().
2) global_assign_ctrl_assign_mon_per_cpu (assign_mon) forces binding
to an RDTMON_GROUP, requiring users to create an extra monitor
sub-group. Since the kernel-mode group is dedicated (no user tasks),
the ctrl group's own RMID is clean and usable. The extra monitor
group wastes a scarce RMID for no benefit.
Remove the RDTMON_GROUP constraint for assign_mon so it accepts
both RDTCTRL_GROUP and RDTMON_GROUP. The RDTCTRL_GROUP constraint
for inherit_mon is kept (it needs only a CLOSID, not a separate
RMID).
Upstream confirmation:
https://lore.kernel.org/all/1d7c79bf-1e40-4db7-8f66-45f234b6d87e@xxxxxxx/
Signed-off-by: Qinyun Tan <qinyuntan@xxxxxxxxxxxxxxxxx>
Reviewed-by: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 9 ++--
drivers/resctrl/mpam_resctrl.c | 2 +-
fs/resctrl/rdtgroup.c | 55 ++++++++++++++---------
include/linux/resctrl.h | 8 ++--
4 files changed, 45 insertions(+), 29 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 5de02a45b58e2..98bc079024219 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -234,18 +234,21 @@ static void resctrl_kmode_set_one_amd(void *arg)
* resctrl_arch_configure_kmode() - x86/AMD: program PLZA MSR on a CPU subset
* @cpu_mask: CPUs to receive the update (see on_each_cpu_mask() for online subset).
* @closid: CLOSID field written into the MSR with CLOSID_EN set.
- * @rmid: RMID field written into the MSR with RMID_EN set.
+ * @rmid: RMID field written into the MSR (only used when @assign_rmid is true).
+ * @assign_rmid: When true, set RMID_EN so CPL=0 uses the PLZA RMID; when false,
+ * clear RMID_EN so CPL=0 inherits RMID from PQR_ASSOC.
* @enable: Value for the PLZA_EN split field.
*
* Context: Do not call with IRQs off or from IRQ context except as allowed for
* on_each_cpu_mask(); see kernel/smp.c.
*/
-void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid, u32 rmid, bool enable)
+void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid,
+ u32 rmid, bool assign_rmid, bool enable)
{
union msr_pqr_plza_assoc plza = { 0 };
plza.split.rmid = rmid;
- plza.split.rmid_en = 1;
+ plza.split.rmid_en = assign_rmid ? 1 : 0;
plza.split.closid = closid;
plza.split.closid_en = 1;
plza.split.plza_en = enable;
diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index fc2b3f508c039..dcf0339d92e5b 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -166,7 +166,7 @@ void resctrl_arch_get_kmode_support(struct resctrl_kmode_cfg *kcfg)
}
void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid,
- u32 rmid, bool enable)
+ u32 rmid, bool assign_rmid, bool enable)
{
}
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 0b2606f10e2e9..1d9bd34eb9cdd 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -457,6 +457,7 @@ static int rdtgroup_kmode_cpus_show(struct kernfs_open_file *of, struct seq_file
static int kmode_cpus_write(struct rdtgroup *rdtgrp, cpumask_var_t newmask,
cpumask_var_t tmpmask)
{
+ bool assign_rmid = (resctrl_kcfg.kmode_cur == BIT(GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU));
u32 closid, rmid;
if (rdtgrp->type == RDTMON_GROUP) {
@@ -475,18 +476,22 @@ static int kmode_cpus_write(struct rdtgroup *rdtgrp, cpumask_var_t newmask,
*/
cpumask_andnot(tmpmask, cpu_online_mask, newmask);
if (!cpumask_empty(tmpmask))
- resctrl_arch_configure_kmode(tmpmask, closid, rmid, false);
- resctrl_arch_configure_kmode(newmask, closid, rmid, true);
+ resctrl_arch_configure_kmode(tmpmask, closid, rmid,
+ assign_rmid, false);
+ resctrl_arch_configure_kmode(newmask, closid, rmid,
+ assign_rmid, true);
} else {
/* CPUs dropped from this group: old & ~newmask. */
cpumask_andnot(tmpmask, &rdtgrp->kmode_cpu_mask, newmask);
if (!cpumask_empty(tmpmask))
- resctrl_arch_configure_kmode(tmpmask, closid, rmid, false);
+ resctrl_arch_configure_kmode(tmpmask, closid, rmid,
+ assign_rmid, false);
/* CPUs newly added: newmask & ~old. */
cpumask_andnot(tmpmask, newmask, &rdtgrp->kmode_cpu_mask);
if (!cpumask_empty(tmpmask))
- resctrl_arch_configure_kmode(tmpmask, closid, rmid, true);
+ resctrl_arch_configure_kmode(tmpmask, closid, rmid,
+ assign_rmid, true);
}
cpumask_copy(&rdtgrp->kmode_cpu_mask, newmask);
@@ -1305,29 +1310,32 @@ static void resctrl_kmode_files_set_visible(struct rdtgroup *rdtgrp, bool visibl
/**
* rdtgroup_config_kmode() - Push @rdtgrp's kernel CLOSID/RMID to hardware
* @rdtgrp: Resctrl group whose CLOSID/RMID should be programmed.
+ * @kmode: Kernel-mode policy being activated, as a
+ * BIT(&enum resctrl_kernel_modes) value. Used to determine
+ * the RMID_EN setting: BIT(GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU)
+ * sets RMID_EN so CPL=0 uses the PLZA RMID; other modes clear it
+ * so CPL=0 inherits the user process's RMID from PQR_ASSOC.
*
* Derives CLOSID/RMID from @rdtgrp->type:
* - RDTMON_GROUP: parent control group's CLOSID with the monitor group's RMID.
- * - RDTCTRL_GROUP: the control group's own CLOSID and default RMID.
+ * - RDTCTRL_GROUP: the control group's own CLOSID and RMID.
*
* Calls resctrl_arch_configure_kmode() with the kernel-mode binding enabled
* on the online subset of @rdtgrp->kmode_cpu_mask (or all online CPUs when
* that mask is empty), and disabled on the complementary online CPUs so
* stale enable bits from a previously bound group are cleared in the same
- * reprogram step. The caller (resctrl_kernel_mode_write()) is responsible
- * for validating that the (kmode, group type) pair is permitted before
- * invoking this helper.
+ * reprogram step.
*
* Context: Caller must hold rdtgroup_mutex.
*
* Return: 0 on success, -EINVAL for a pseudo-locked group, -ENOMEM if
* cpumask allocation fails.
*/
-static int rdtgroup_config_kmode(struct rdtgroup *rdtgrp)
+static int rdtgroup_config_kmode(struct rdtgroup *rdtgrp, u32 kmode)
{
cpumask_var_t enable_mask, disable_mask;
u32 closid, rmid;
- bool need_disable;
+ bool need_disable, assign_rmid;
if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
rdt_last_cmd_puts("Resource group is pseudo-locked\n");
@@ -1363,11 +1371,15 @@ static int rdtgroup_config_kmode(struct rdtgroup *rdtgrp)
cpumask_andnot(disable_mask, cpu_online_mask, &rdtgrp->kmode_cpu_mask);
}
+ assign_rmid = (kmode == BIT(GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU));
+
if (!cpumask_empty(enable_mask))
- resctrl_arch_configure_kmode(enable_mask, closid, rmid, true);
+ resctrl_arch_configure_kmode(enable_mask, closid, rmid,
+ assign_rmid, true);
if (need_disable && !cpumask_empty(disable_mask))
- resctrl_arch_configure_kmode(disable_mask, closid, rmid, false);
+ resctrl_arch_configure_kmode(disable_mask, closid, rmid,
+ assign_rmid, false);
rdtgrp->kmode = true;
resctrl_kmode_files_set_visible(rdtgrp, true);
@@ -1409,6 +1421,7 @@ static int rdtgroup_config_kmode(struct rdtgroup *rdtgrp)
static int rdtgroup_config_kmode_clear(struct rdtgroup *rdtgrp, int kmode)
{
cpumask_var_t disable_mask;
+ bool assign_rmid;
u32 closid, rmid;
if (!rdtgrp)
@@ -1428,12 +1441,15 @@ static int rdtgroup_config_kmode_clear(struct rdtgroup *rdtgrp, int kmode)
rmid = rdtgrp->mon.rmid;
}
+ assign_rmid = (kmode == BIT(GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU));
+
if (cpumask_empty(&rdtgrp->kmode_cpu_mask))
cpumask_copy(disable_mask, cpu_online_mask);
else
cpumask_copy(disable_mask, &rdtgrp->kmode_cpu_mask);
- resctrl_arch_configure_kmode(disable_mask, closid, rmid, false);
+ resctrl_arch_configure_kmode(disable_mask, closid, rmid,
+ assign_rmid, false);
free_cpumask_var(disable_mask);
out_clear:
@@ -1665,19 +1681,14 @@ static ssize_t resctrl_kernel_mode_write(struct kernfs_open_file *of,
/*
* global_assign_ctrl_assign_mon_per_cpu binds one CLOSID and RMID for
- * all kernel work (Documentation/filesystems/resctrl.rst uses
- * "<ctrl>/<mon>/", i.e. an RDTMON_GROUP).
+ * all kernel work. Both RDTCTRL_GROUP and RDTMON_GROUP are accepted:
+ * a control group is sufficient (its own CLOSID and RMID are used) and
+ * avoids wasting an RMID on an unnecessary monitor sub-group.
*
* global_assign_ctrl_inherit_mon_per_cpu assigns one CLOSID globally
* while leaving RMID inheritance to user contexts; that uses the
* control group's CLOSID slot only, i.e. an RDTCTRL_GROUP.
*/
- if (kmode == BIT(GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU) &&
- rdtgrp->type != RDTMON_GROUP) {
- rdt_last_cmd_puts("global_assign_ctrl_assign_mon_per_cpu requires a monitor group\n");
- ret = -EINVAL;
- goto out_unlock;
- }
if (kmode == BIT(GLOBAL_ASSIGN_CTRL_INHERIT_MON_PER_CPU) &&
rdtgrp->type != RDTCTRL_GROUP) {
rdt_last_cmd_puts("global_assign_ctrl_inherit_mon_per_cpu requires a control group\n");
@@ -1693,7 +1704,7 @@ static ssize_t resctrl_kernel_mode_write(struct kernfs_open_file *of,
}
if (kmode != BIT(INHERIT_CTRL_AND_MON)) {
- ret = rdtgroup_config_kmode(rdtgrp);
+ ret = rdtgroup_config_kmode(rdtgrp, kmode);
if (ret) {
rdt_last_cmd_puts("Kernel mode change failed\n");
goto out_unlock;
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index e2135f0d42506..256449a0c92ff 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -724,11 +724,13 @@ void resctrl_arch_get_kmode_support(struct resctrl_kmode_cfg *kcfg);
* resctrl_arch_configure_kmode() - Program MSR_IA32_PQR_PLZA_ASSOC on CPUs in @cpu_mask
* @cpu_mask: Target CPUs; on_each_cpu_mask() applies the callback on the online subset.
* @closid: CLOSID written to the MSR with CLOSID_EN set.
- * @rmid: RMID written to the MSR with RMID_EN set.
+ * @rmid: RMID written to the MSR (only used when @assign_rmid is true).
+ * @assign_rmid: When true, set RMID_EN so CPL=0 uses the PLZA RMID; when false,
+ * clear RMID_EN so CPL=0 inherits RMID from PQR_ASSOC.
* @enable: PLZA_EN field value for this update.
*/
-void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid, u32 rmid,
- bool enable);
+void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid,
+ u32 rmid, bool assign_rmid, bool enable);
extern unsigned int resctrl_rmid_realloc_threshold;
extern unsigned int resctrl_rmid_realloc_limit;
--
2.43.7