[RFC PATCH v3 02/14] iommu/riscv: Prepare domain bonds for outer locking

[Andrew Jones]

IRQ bypass will serialize attachment under a raw spinlock. Bond updates
retain their own lock, so make it raw for safe PREEMPT_RT nesting.

MSI forwarding will acquire the MSI table lock under the hardirq-safe
IRQ descriptor lock. Nesting the bond lock below the MSI table lock
therefore requires IRQ protection even for domains without an MSI
table, where attachment takes only the bond lock. Use irqsave/irqrestore
in both bond helpers to avoid a HARDIRQ-safe to HARDIRQ-unsafe lock
dependency.

Also split allocation from list insertion so a future outer lock can be
taken after the sleeping allocation.

No functional change intended.

Signed-off-by: Andrew Jones <andrew.jones at oss.qualcomm.com>
---
 drivers/iommu/riscv/iommu.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index 3bbb4d0d0a85..09ec8c3e4a72 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -858,7 +858,7 @@ struct riscv_iommu_domain {
 		struct pt_iommu_riscv_64 riscvpt;
 	};
 	struct list_head bonds;
-	spinlock_t lock;		/* protect bonds list updates. */
+	raw_spinlock_t lock;		/* protect bonds list updates. */
 	struct mutex mutex;		/* serialize domain state updates */
 	int pscid;
 	int gscid;
@@ -896,34 +896,27 @@ struct riscv_iommu_bond {
 	struct device *dev;
 };
 
-static int riscv_iommu_bond_link(struct riscv_iommu_domain *domain,
-				 struct device *dev)
+static void riscv_iommu_bond_link(struct riscv_iommu_domain *domain,
+				  struct riscv_iommu_bond *bond)
 {
-	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
-	struct riscv_iommu_bond *bond;
+	struct riscv_iommu_device *iommu = dev_to_iommu(bond->dev);
 	struct list_head *bonds;
-
-	bond = kzalloc_obj(*bond);
-	if (!bond)
-		return -ENOMEM;
-	bond->dev = dev;
+	unsigned long flags;
 
 	/*
 	 * List of devices attached to the domain is arranged based on
 	 * managed IOMMU device.
 	 */
 
-	spin_lock(&domain->lock);
+	raw_spin_lock_irqsave(&domain->lock, flags);
 	list_for_each(bonds, &domain->bonds)
 		if (dev_to_iommu(list_entry(bonds, struct riscv_iommu_bond, list)->dev) == iommu)
 			break;
 	list_add_rcu(&bond->list, bonds);
-	spin_unlock(&domain->lock);
+	raw_spin_unlock_irqrestore(&domain->lock, flags);
 
 	/* Synchronize with riscv_iommu_iotlb_inval() sequence. See comment below. */
 	smp_mb();
-
-	return 0;
 }
 
 static void riscv_iommu_bond_unlink(struct riscv_iommu_domain *domain,
@@ -932,12 +925,13 @@ static void riscv_iommu_bond_unlink(struct riscv_iommu_domain *domain,
 	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
 	struct riscv_iommu_bond *bond, *found = NULL;
 	struct riscv_iommu_command cmd;
+	unsigned long flags;
 	int count = 0;
 
 	if (!domain)
 		return;
 
-	spin_lock(&domain->lock);
+	raw_spin_lock_irqsave(&domain->lock, flags);
 	list_for_each_entry(bond, &domain->bonds, list) {
 		if (found && count)
 			break;
@@ -948,7 +942,7 @@ static void riscv_iommu_bond_unlink(struct riscv_iommu_domain *domain,
 	}
 	if (found)
 		list_del_rcu(&found->list);
-	spin_unlock(&domain->lock);
+	raw_spin_unlock_irqrestore(&domain->lock, flags);
 	kfree_rcu(found, rcu);
 
 	/*
@@ -1391,6 +1385,7 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
 	struct riscv_iommu_domain *domain = iommu_domain_to_riscv(iommu_domain);
 	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
 	struct riscv_iommu_info *info = dev_iommu_priv_get(dev);
+	struct riscv_iommu_bond *bond;
 	struct pt_iommu_riscv_64_hw_info pt_info;
 	struct riscv_iommu_dc dc = {0};
 	int ret;
@@ -1421,9 +1416,12 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
 	dc.ta = FIELD_PREP(RISCV_IOMMU_PC_TA_PSCID, domain->pscid) |
 	     RISCV_IOMMU_PC_TA_V;
 
-	if (riscv_iommu_bond_link(domain, dev))
+	bond = kzalloc_obj(*bond);
+	if (!bond)
 		return -ENOMEM;
+	bond->dev = dev;
 
+	riscv_iommu_bond_link(domain, bond);
 	riscv_iommu_iodir_update(iommu, dev, &dc);
 	riscv_iommu_bond_unlink(info->domain, dev);
 	info->domain = domain;
@@ -1475,7 +1473,7 @@ riscv_iommu_domain_alloc_paging_flags(struct device *dev, u32 flags,
 		return ERR_PTR(-ENOMEM);
 
 	INIT_LIST_HEAD_RCU(&domain->bonds);
-	spin_lock_init(&domain->lock);
+	raw_spin_lock_init(&domain->lock);
 	mutex_init(&domain->mutex);
 	iommu = dev_to_iommu(dev);
 	cfg.common.hw_max_oasz_lg2 = 56;
-- 
2.43.0