[PATCH v5 17/18] iommu/arm-smmu-v3: Thread arm_smmu_master_domain on a per-master list

[Nicolin Chen]

A subsequent change needs to enumerate, from the CMDQ error path in atomic
context, every domain a master is attached to so it can mark this master's
ATS entries broken in each domain's invs after an ATC invalidation timeout.
The existing per-domain smmu_domain->devices list tracks the inverse
direction (masters in a given domain), so introduce a per-master list.

Add a second list_head master_elm to arm_smmu_master_domain, threaded onto
a new master->master_domains list under master_domains_lock. The CMDQ error
path walks the list while holding smmu->streams_lock; that path runs under
the invs->rwlock read side, which is itself sleepable on PREEMPT_RT, so a
plain spinlock_t suffices for both. The attach and detach sites now take it
with spin_lock(), nested inside the existing devices_lock critical section
that already disables IRQs; it is a leaf in the lock order, so no inversion
is introduced.

No functional change.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Nicolin Chen <nicolinc at nvidia.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 4 ++++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index 8eb5684696316..4aa0c5fedff71 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -1029,6 +1029,9 @@ struct arm_smmu_master {
 	struct arm_smmu_vmaster		*vmaster; /* use smmu->streams_mutex */
 	/* Locked by the iommu core using the group mutex */
 	struct arm_smmu_ctx_desc_cfg	cd_table;
+	struct list_head		master_domains;
+	/* Protects master_domains */
+	spinlock_t			master_domains_lock;
 	unsigned int			num_streams;
 	bool				ats_enabled : 1;
 	bool				ste_ats_enabled : 1;
@@ -1123,6 +1126,7 @@ struct arm_smmu_invs *arm_smmu_invs_purge(struct arm_smmu_invs *invs);
 
 struct arm_smmu_master_domain {
 	struct list_head devices_elm;
+	struct list_head master_elm;
 	struct arm_smmu_master *master;
 	/*
 	 * For nested domains the master_domain is threaded onto the S2 parent,
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 0697bbc558d0e..fd9a095154c72 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -3372,6 +3372,9 @@ static void arm_smmu_remove_master_domain(struct arm_smmu_master *master,
 						    ssid, nested_ats_flush);
 	if (master_domain) {
 		list_del(&master_domain->devices_elm);
+		spin_lock(&master->master_domains_lock);
+		list_del(&master_domain->master_elm);
+		spin_unlock(&master->master_domains_lock);
 		if (master->ats_enabled)
 			atomic_dec(&smmu_domain->nr_ats_masters);
 	}
@@ -3622,6 +3625,9 @@ int arm_smmu_attach_prepare(struct arm_smmu_attach_state *state,
 		if (state->ats_enabled)
 			atomic_inc(&smmu_domain->nr_ats_masters);
 		list_add(&master_domain->devices_elm, &smmu_domain->devices);
+		spin_lock(&master->master_domains_lock);
+		list_add(&master_domain->master_elm, &master->master_domains);
+		spin_unlock(&master->master_domains_lock);
 		spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
 
 		arm_smmu_install_new_domain_invs(state);
@@ -4346,6 +4352,8 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
 	master->dev = dev;
 	master->smmu = smmu;
 	dev_iommu_priv_set(dev, master);
+	INIT_LIST_HEAD(&master->master_domains);
+	spin_lock_init(&master->master_domains_lock);
 
 	ret = arm_smmu_insert_master(smmu, master);
 	if (ret)
-- 
2.43.0