[PATCH 18/33] arm_mpam: Reset MSC controls from cpuhp callbacks

Ben Horgan
2025-11-07T12:37:02Z

From: James Morse <james.morse@arm.com>

When a CPU comes online, it may bring a newly accessible MSC with
it. Only the default partid has its value reset by hardware, and
even then the MSC might not have been reset since its config was
previously dirtied. e.g. Kexec.

Any in-use partid must have its configuration restored, or reset.
In-use partids may be held in caches and evicted later.

MSC are also reset when CPUs are taken offline to cover cases where
firmware doesn't reset the MSC over reboot using UEFI, or kexec
where there is no firmware involvement.

If the configuration for a RIS has not been touched since it was
brought online, it does not need resetting again.

To reset, write the maximum values for all discovered controls.

CC: Rohit Mathew <Rohit.Mathew@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v3:
Add tags - thanks!
---
drivers/resctrl/mpam_devices.c | 109 ++++++++++++++++++++++++++++++++
drivers/resctrl/mpam_internal.h | 3 +
2 files changed, 112 insertions(+)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 7c02b918fa0f..6a01247317b7 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -7,6 +7,7 @@
#include <linux/atomic.h>
#include <linux/arm_mpam.h>
#include <linux/bitfield.h>
+#include <linux/bitmap.h>
#include <linux/cacheinfo.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
@@ -753,8 +754,104 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
return 0;
}

+static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
+{
+ u32 num_words, msb;
+ u32 bm = ~0;
+ int i;
+
+ lockdep_assert_held(&msc->part_sel_lock);
+
+ if (wd == 0)
+ return;
+
+ /*
+ * Write all ~0 to all but the last 32bit-word, which may
+ * have fewer bits...
+ */
+ num_words = DIV_ROUND_UP(wd, 32);
+ for (i = 0; i < num_words - 1; i++, reg += sizeof(bm))
+ __mpam_write_reg(msc, reg, bm);
+
+ /*
+ * ....and then the last (maybe) partial 32bit word. When wd is a
+ * multiple of 32, msb should be 31 to write a full 32bit word.
+ */
+ msb = (wd - 1) % 32;
+ bm = GENMASK(msb, 0);
+ __mpam_write_reg(msc, reg, bm);
+}
+
+static void mpam_reset_ris_partid(struct mpam_msc_ris *ris, u16 partid)
+{
+ 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_mbw_part, rprops))
+ mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM, rprops->mbw_pbm_bits);
+
+ if (mpam_has_feature(mpam_feat_mbw_min, rprops))
+ 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);
+
+ mutex_unlock(&msc->part_sel_lock);
+}
+
+static void mpam_reset_ris(struct mpam_msc_ris *ris)
+{
+ u16 partid, partid_max;
+
+ WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu)));
+
+ if (ris->in_reset_state)
+ return;
+
+ spin_lock(&partid_max_lock);
+ partid_max = mpam_partid_max;
+ spin_unlock(&partid_max_lock);
+ for (partid = 0; partid <= partid_max; partid++)
+ mpam_reset_ris_partid(ris, partid);
+}
+
+static void mpam_reset_msc(struct mpam_msc *msc, bool online)
+{
+ struct mpam_msc_ris *ris;
+
+ list_for_each_entry_srcu(ris, &msc->ris, msc_list, srcu_read_lock_held(&mpam_srcu)) {
+ mpam_reset_ris(ris);
+
+ /*
+ * Set in_reset_state when coming online. The reset state
+ * for non-zero partid may be lost while the CPUs are offline.
+ */
+ ris->in_reset_state = online;
+ }
+}
+
static int mpam_cpu_online(unsigned int cpu)
{
+ struct mpam_msc *msc;
+
+ guard(srcu)(&mpam_srcu);
+ list_for_each_entry_srcu(msc, &mpam_all_msc, all_msc_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ if (!cpumask_test_cpu(cpu, &msc->accessibility))
+ continue;
+
+ if (atomic_fetch_inc(&msc->online_refs) == 0)
+ mpam_reset_msc(msc, true);
+ }
+
return 0;
}

@@ -793,6 +890,18 @@ static int mpam_discovery_cpu_online(unsigned int cpu)

static int mpam_cpu_offline(unsigned int cpu)
{
+ struct mpam_msc *msc;
+
+ guard(srcu)(&mpam_srcu);
+ list_for_each_entry_srcu(msc, &mpam_all_msc, all_msc_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ if (!cpumask_test_cpu(cpu, &msc->accessibility))
+ continue;
+
+ if (atomic_dec_and_test(&msc->online_refs))
+ mpam_reset_msc(msc, false);
+ }
+
return 0;
}

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 1a95b2897ac1..1ad62f13bfb3 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -5,6 +5,7 @@
#define MPAM_INTERNAL_H

#include <linux/arm_mpam.h>
+#include <linux/atomic.h>
#include <linux/bitmap.h>
#include <linux/cpumask.h>
#include <linux/io.h>
@@ -45,6 +46,7 @@ struct mpam_msc {
enum mpam_msc_iface iface;
u32 nrdy_usec;
cpumask_t accessibility;
+ atomic_t online_refs;

/*
* probe_lock is only taken during discovery. After discovery these
@@ -196,6 +198,7 @@ struct mpam_msc_ris {
u8 ris_idx;
u64 idr;
struct mpam_props props;
+ bool in_reset_state;

cpumask_t affinity;

--
2.43.0