[RFC PATCH v3 11/14] iommu/riscv: Prepare info->domain for concurrent RCU access

[Andrew Jones]

Upcoming interrupt-remapping callbacks need to resolve a device's
currently attached domain from IRQ context, concurrent with domain
switches.

Protect info->domain with RCU and wait for readers before freeing paging
domains. Provide an RCU accessor for the domain-owned MSI table so
interrupt-remapping code does not need the private domain definition.

Use the stable old domain supplied by the attachment callback when
unlinking its bond instead of dereferencing the now RCU-protected
info->domain.

Signed-off-by: Andrew Jones <andrew.jones at oss.qualcomm.com>
---
 drivers/iommu/riscv/iommu.c | 34 +++++++++++++++++++++++++---------
 drivers/iommu/riscv/iommu.h |  5 ++++-
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index 7a8b40d311ea..514470291fd9 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -869,6 +869,16 @@ PT_IOMMU_CHECK_DOMAIN(struct riscv_iommu_domain, riscvpt.iommu, domain);
 #define iommu_domain_to_riscv(iommu_domain) \
 	container_of(iommu_domain, struct riscv_iommu_domain, domain)
 
+struct riscv_iommu_msi_table *riscv_iommu_msi_table_rcu(struct riscv_iommu_info *info)
+{
+	struct riscv_iommu_domain *domain;
+
+	lockdep_assert_in_rcu_read_lock();
+	domain = rcu_dereference(info->domain);
+
+	return domain ? &domain->msi_table : NULL;
+}
+
 static struct riscv_iommu_msi_table *riscv_iommu_domain_msi_table(struct iommu_domain *iommu_domain)
 {
 	struct riscv_iommu_domain *domain;
@@ -968,18 +978,22 @@ static void riscv_iommu_bond_link(struct riscv_iommu_domain *domain,
 	smp_mb();
 }
 
-static void riscv_iommu_bond_unlink(struct riscv_iommu_domain *domain,
+static void riscv_iommu_bond_unlink(struct iommu_domain *iommu_domain,
 				    struct device *dev)
 {
-	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
+	struct riscv_iommu_domain *domain;
+	struct riscv_iommu_device *iommu;
 	struct riscv_iommu_bond *bond, *found = NULL;
 	struct riscv_iommu_command cmd;
 	unsigned long flags;
 	int count = 0;
 
-	if (!domain)
+	if (!iommu_domain || !(iommu_domain->type & __IOMMU_DOMAIN_PAGING))
 		return;
 
+	domain = iommu_domain_to_riscv(iommu_domain);
+	iommu = dev_to_iommu(dev);
+
 	raw_spin_lock_irqsave(&domain->lock, flags);
 	list_for_each_entry(bond, &domain->bonds, list) {
 		if (found && count)
@@ -1415,6 +1429,8 @@ static void riscv_iommu_free_paging_domain(struct iommu_domain *iommu_domain)
 
 	WARN_ON(!list_empty(&domain->bonds));
 
+	synchronize_rcu();
+
 	if (domain->pscid > 0)
 		ida_free(&riscv_iommu_pscids, domain->pscid);
 	if (domain->gscid > 0)
@@ -1577,8 +1593,8 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
 	info->dc = dc;
 	riscv_iommu_bond_link(domain, bond);
 	riscv_iommu_iodir_update(dev, &info->dc);
-	riscv_iommu_bond_unlink(info->domain, dev);
-	info->domain = domain;
+	riscv_iommu_bond_unlink(old, dev);
+	rcu_assign_pointer(info->domain, domain);
 	riscv_iommu_msi_tables_unlock(old, iommu_domain, flags);
 
 	return 0;
@@ -1732,8 +1748,8 @@ static int riscv_iommu_attach_blocking_domain(struct iommu_domain *iommu_domain,
 	flags = riscv_iommu_msi_tables_lock(old, NULL);
 	info->dc = dc;
 	riscv_iommu_iodir_update(dev, &info->dc);
-	riscv_iommu_bond_unlink(info->domain, dev);
-	info->domain = NULL;
+	riscv_iommu_bond_unlink(old, dev);
+	rcu_assign_pointer(info->domain, NULL);
 	riscv_iommu_msi_tables_unlock(old, NULL, flags);
 
 	return 0;
@@ -1760,8 +1776,8 @@ static int riscv_iommu_attach_identity_domain(struct iommu_domain *iommu_domain,
 	flags = riscv_iommu_msi_tables_lock(old, NULL);
 	info->dc = dc;
 	riscv_iommu_iodir_update(dev, &info->dc);
-	riscv_iommu_bond_unlink(info->domain, dev);
-	info->domain = NULL;
+	riscv_iommu_bond_unlink(old, dev);
+	rcu_assign_pointer(info->domain, NULL);
 	riscv_iommu_msi_tables_unlock(old, NULL, flags);
 
 	return 0;
diff --git a/drivers/iommu/riscv/iommu.h b/drivers/iommu/riscv/iommu.h
index 4c1c681ba2a2..ed973979d795 100644
--- a/drivers/iommu/riscv/iommu.h
+++ b/drivers/iommu/riscv/iommu.h
@@ -16,6 +16,7 @@
 #include <linux/types.h>
 #include <linux/iopoll.h>
 #include <linux/irqdomain.h>
+#include <linux/rcupdate.h>
 #include <linux/sizes.h>
 
 #include "iommu-bits.h"
@@ -85,7 +86,7 @@ struct riscv_iommu_msi_table {
 
 /* Private IOMMU data for managed devices, dev_iommu_priv_* */
 struct riscv_iommu_info {
-	struct riscv_iommu_domain *domain;
+	struct riscv_iommu_domain __rcu *domain;
 	struct riscv_iommu_dc dc;
 	struct irq_domain *old_msi_parent;
 	unsigned int nr_forwarded_irqs;
@@ -100,6 +101,8 @@ int riscv_iommu_init(struct riscv_iommu_device *iommu);
 void riscv_iommu_remove(struct riscv_iommu_device *iommu);
 void riscv_iommu_disable(struct riscv_iommu_device *iommu);
 
+/* Caller must hold rcu_read_lock() while using the returned pointer. */
+struct riscv_iommu_msi_table *riscv_iommu_msi_table_rcu(struct riscv_iommu_info *info);
 void riscv_iommu_msi_table_inval(struct riscv_iommu_msi_table *msi_table, unsigned long addr);
 void riscv_iommu_msi_table_inval_all(struct riscv_iommu_msi_table *msi_table);
 void riscv_iommu_msi_table_update(struct riscv_iommu_msi_table *msi_table, bool activate);
-- 
2.43.0