On Mon, Oct 27, 2025 at 9:48 AM Shaopeng Tan (Fujitsu)
[off-list ref] wrote:

Hello James,

quoted

When CPUs come online the MSC's original configuration should be restored.

Add struct mpam_config to hold the configuration. This has a bitmap of
features that were modified. Once the maximum partid is known, allocate a
configuration array for each component, and reprogram each RIS configuration
from this.

CC: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
---
Changes since v2:
 * Call mpam_init_reset_cfg() on alloated config as 0 is not longer correct.
 * init_garbage() on each config - the array has to be freed in one go, but
   otherwise this looks weird.
 * Use struct initialiser in mpam_init_reset_cfg(),
 * Moved int err definition.
 * Removed srcu lock taking based on squinting at the only caller.
 * Moved config reset to mpam_reset_component_cfg() for re-use in
   mpam_reset_component_locked(), previous memset() was not enough
since zero
   no longer means reset.

Changes since v1:
 * Switched entry_rcu to srcu versions.

Changes since RFC:
 * Added a comment about the ordering around max_partid.
 * Allocate configurations after interrupts are registered to reduce churn.
 * Added mpam_assert_partid_sizes_fixed();
 * Make reset use an all-ones instead of zero config.
---
 drivers/resctrl/mpam_devices.c  | 284
+++++++++++++++++++++++++++++---
drivers/resctrl/mpam_internal.h |  23 +++
 2 files changed, 287 insertions(+), 20 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index ab37ed1fb5de..e990ef67df5b 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c

@@ -118,6 +118,17 @@ static inline void init_garbage(struct mpam_garbage

*garbage)  {
      init_llist_node(&garbage->llist);
 }
+
+/*
+ * Once mpam is enabled, new requestors cannot further reduce the
+available
+ * partid. Assert that the size is fixed, and new requestors will be
+turned
+ * away.
+ */
+static void mpam_assert_partid_sizes_fixed(void)
+{
+     WARN_ON_ONCE(!partid_max_published);
+}
+
 static u32 __mpam_read_reg(struct mpam_msc *msc, u16 reg)  {
      WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(),
&msc->accessibility)); @@ -366,12 +377,16 @@ static void
mpam_class_destroy(struct mpam_class *class)
      add_to_garbage(class);
 }

+static void __destroy_component_cfg(struct mpam_component *comp);
+
 static void mpam_comp_destroy(struct mpam_component *comp)  {
      struct mpam_class *class = comp->class;

      lockdep_assert_held(&mpam_list_lock);

+     __destroy_component_cfg(comp);
+
      list_del_rcu(&comp->class_list);
      add_to_garbage(comp);

@@ -812,48 +827,102 @@ static void mpam_reset_msc_bitmap(struct

mpam_msc *msc, u16 reg, u16 wd)
      __mpam_write_reg(msc, reg, bm);
 }

-static void mpam_reset_ris_partid(struct mpam_msc_ris *ris, u16 partid)
+/* Called via IPI. Call while holding an SRCU reference */ static void
+mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid,
+                                   struct mpam_config *cfg)
 {
      struct mpam_msc *msc = ris->vmsc->msc;
      struct mpam_props *rprops = &ris->props;

-     WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu)));
-
      mutex_lock(&msc->part_sel_lock);
      __mpam_part_sel(ris->ris_idx, partid, msc);

-     if (mpam_has_feature(mpam_feat_cpor_part, rprops))
-             mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM,
rprops->cpbm_wd);
+     if (mpam_has_feature(mpam_feat_cpor_part, rprops) &&
+         mpam_has_feature(mpam_feat_cpor_part, cfg)) {
+             if (cfg->reset_cpbm)
+                     mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM,
+                                           rprops->cpbm_wd);
+             else
+                     mpam_write_partsel_reg(msc, CPBM, cfg->cpbm);
+     }

-     if (mpam_has_feature(mpam_feat_mbw_part, rprops))
-             mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM,
rprops->mbw_pbm_bits);
+     if (mpam_has_feature(mpam_feat_mbw_part, rprops) &&
+         mpam_has_feature(mpam_feat_mbw_part, cfg)) {
+             if (cfg->reset_mbw_pbm)
+                     mpam_reset_msc_bitmap(msc,
MPAMCFG_MBW_PBM,
+                                           rprops->mbw_pbm_bits);
+             else
+                     mpam_write_partsel_reg(msc, MBW_PBM,
cfg->mbw_pbm);
+     }

-     if (mpam_has_feature(mpam_feat_mbw_min, rprops))
+     if (mpam_has_feature(mpam_feat_mbw_min, rprops) &&
+         mpam_has_feature(mpam_feat_mbw_min, cfg))
              mpam_write_partsel_reg(msc, MBW_MIN, 0);

-     if (mpam_has_feature(mpam_feat_mbw_max, rprops))
-             mpam_write_partsel_reg(msc, MBW_MAX,
MPAMCFG_MBW_MAX_MAX);
+     if (mpam_has_feature(mpam_feat_mbw_max, rprops) &&
+         mpam_has_feature(mpam_feat_mbw_max, cfg))
+             mpam_write_partsel_reg(msc, MBW_MAX, cfg->mbw_max);

      mutex_unlock(&msc->part_sel_lock);
 }

+struct reprogram_ris {
+     struct mpam_msc_ris *ris;
+     struct mpam_config *cfg;
+};
+
+/* Call with MSC lock held */
+static int mpam_reprogram_ris(void *_arg) {
+     u16 partid, partid_max;
+     struct reprogram_ris *arg = _arg;
+     struct mpam_msc_ris *ris = arg->ris;
+     struct mpam_config *cfg = arg->cfg;
+
+     if (ris->in_reset_state)
+             return 0;
+
+     spin_lock(&partid_max_lock);
+     partid_max = mpam_partid_max;
+     spin_unlock(&partid_max_lock);
+     for (partid = 0; partid <= partid_max + 1; partid++)
+             mpam_reprogram_ris_partid(ris, partid, cfg);
+
+     return 0;
+}
+
+static void mpam_init_reset_cfg(struct mpam_config *reset_cfg) {
+     *reset_cfg = (struct mpam_config) {
+             .cpbm = ~0,
+             .mbw_pbm = ~0,
+             .mbw_max = MPAMCFG_MBW_MAX_MAX,

When rdtgroup_schemata_show() is called, the "cpbm" value is output to the schema file.
Since bitmap lengths are chip-dependent, I think we just need to reset the bitmap length portion.
Otherwise, 0xffffffff(u32) will be output from the schemata file.

When I apply additional patches to add the mpam_resctrl.c stuff I
notice this too:

# grep L3 schemata
L3:1=ffffffff
# cat info/L3/shareable_bits
ffff

I noticed that new groups also get a too-long cbm as long as any other
groups have a too-long cbm. Maybe this out-of-range value is bleeding
into new groups in __init_one_rdt_domain() when it calls
resctrl_arch_get_config() on all other groups.

-Peter