Message-Id: <20250711183648.30766-23-james.morse@arm.com>
Date: Fri, 11 Jul 2025 18:36:34 +0000
From: James Morse <james.morse@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Cc: Rob Herring <robh@...nel.org>,
	Ben Horgan <ben.horgan@....com>,
	Rohit Mathew <rohit.mathew@....com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	Zeng Heng <zengheng4@...wei.com>,
	Lecopzer Chen <lecopzerc@...dia.com>,
	Carl Worth <carl@...amperecomputing.com>,
	shameerali.kolothum.thodi@...wei.com,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	lcherian@...vell.com,
	bobo.shaobowang@...wei.com,
	tan.shaopeng@...itsu.com,
	baolin.wang@...ux.alibaba.com,
	Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>,
	peternewman@...gle.com,
	dfustini@...libre.com,
	amitsinght@...vell.com,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>,
	Dave Martin <dave.martin@....com>,
	Koba Ko <kobak@...dia.com>,
	James Morse <james.morse@....com>,
	Rohit Mathew <Rohit.Mathew@....com>
Subject: [RFC PATCH 22/36] arm_mpam: Reset MSC controls from cpu hp callbacks

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 dirtyied. 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@....com>
Signed-off-by: James Morse <james.morse@....com>
---
 drivers/platform/arm64/mpam/mpam_devices.c  | 124 +++++++++++++++++++-
 drivers/platform/arm64/mpam/mpam_internal.h |   8 ++
 2 files changed, 131 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/mpam_devices.c
index 7b042a35405a..d014dbe0ab96 100644
--- a/drivers/platform/arm64/mpam/mpam_devices.c
+++ b/drivers/platform/arm64/mpam/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>
@@ -849,8 +850,116 @@ 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);
+	if (bm)
+		__mpam_write_reg(msc, reg, bm);
+}
+
+static void mpam_reset_ris_partid(struct mpam_msc_ris *ris, u16 partid)
+{
+	u16 bwa_fract = MPAMCFG_MBW_MAX_MAX;
+	struct mpam_msc *msc = ris->vmsc->msc;
+	struct mpam_props *rprops = &ris->props;
+
+	mpam_assert_srcu_read_lock_held();
+
+	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, bwa_fract);
+
+	if (mpam_has_feature(mpam_feat_mbw_prop, rprops))
+		mpam_write_partsel_reg(msc, MBW_PROP, bwa_fract);
+	mutex_unlock(&msc->part_sel_lock);
+}
+
+static void mpam_reset_ris(struct mpam_msc_ris *ris)
+{
+	u16 partid, partid_max;
+
+	mpam_assert_srcu_read_lock_held();
+
+	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)
+{
+	int idx;
+	struct mpam_msc_ris *ris;
+
+	mpam_assert_srcu_read_lock_held();
+
+	mpam_mon_sel_outer_lock(msc);
+	idx = srcu_read_lock(&mpam_srcu);
+	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;
+	}
+	srcu_read_unlock(&mpam_srcu, idx);
+	mpam_mon_sel_outer_unlock(msc);
+}
+
 static int mpam_cpu_online(unsigned int cpu)
 {
+	int idx;
+	struct mpam_msc *msc;
+
+	idx = srcu_read_lock(&mpam_srcu);
+	list_for_each_entry_srcu(msc, &mpam_all_msc, glbl_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);
+	}
+	srcu_read_unlock(&mpam_srcu, idx);
+
 	return 0;
 }
 
@@ -886,6 +995,19 @@ static int mpam_discovery_cpu_online(unsigned int cpu)
 
 static int mpam_cpu_offline(unsigned int cpu)
 {
+	int idx;
+	struct mpam_msc *msc;
+
+	idx = srcu_read_lock(&mpam_srcu);
+	list_for_each_entry_srcu(msc, &mpam_all_msc, glbl_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);
+	}
+	srcu_read_unlock(&mpam_srcu, idx);
+
 	return 0;
 }
 
@@ -1419,7 +1541,7 @@ static void mpam_enable_once(void)
 	mpam_register_cpuhp_callbacks(mpam_cpu_online, mpam_cpu_offline);
 
 	printk(KERN_INFO "MPAM enabled with %u partid and %u pmg\n",
-	       mpam_partid_max + 1, mpam_pmg_max + 1);
+		READ_ONCE(mpam_partid_max) + 1, mpam_pmg_max + 1);
 }
 
 /*
diff --git a/drivers/platform/arm64/mpam/mpam_internal.h b/drivers/platform/arm64/mpam/mpam_internal.h
index be56234b84b4..f3cc88136524 100644
--- a/drivers/platform/arm64/mpam/mpam_internal.h
+++ b/drivers/platform/arm64/mpam/mpam_internal.h
@@ -5,6 +5,7 @@
 #define MPAM_INTERNAL_H
 
 #include <linux/arm_mpam.h>
+#include <linux/atomic.h>
 #include <linux/cpumask.h>
 #include <linux/io.h>
 #include <linux/llist.h>
@@ -43,6 +44,7 @@ struct mpam_msc {
 	struct pcc_mbox_chan	*pcc_chan;
 	u32			nrdy_usec;
 	cpumask_t		accessibility;
+	atomic_t		online_refs;
 
 	/*
 	 * probe_lock is only take during discovery. After discovery these
@@ -247,6 +249,7 @@ struct mpam_msc_ris {
 	u8			ris_idx;
 	u64			idr;
 	struct mpam_props	props;
+	bool			in_reset_state;
 
 	cpumask_t		affinity;
 
@@ -266,6 +269,11 @@ struct mpam_msc_ris {
 extern struct srcu_struct mpam_srcu;
 extern struct list_head mpam_classes;
 
+static inline void mpam_assert_srcu_read_lock_held(void)
+{
+	WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu)));
+}
+
 /* System wide partid/pmg values */
 extern u16 mpam_partid_max;
 extern u8 mpam_pmg_max;
-- 
2.39.5

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