[PATCH 2/3] iommu/dma: Support MSIs through nested domains

[Nicolin Chen <nicolinc@xxxxxxxxxx>]

From: Robin Murphy <robin.murphy@xxxxxxx>

Currently, iommu-dma is the only place outside of IOMMUFD and drivers
which might need to be aware of the stage 2 domain encapsulated within
a nested domain. This would be in the legacy-VFIO-style case where we're
using host-managed MSIs with an identity mapping at stage 1, where it is
the underlying stage 2 domain which owns an MSI cookie and holds the
corresponding dynamic mappings. Hook up the new op to resolve what we
need from a nested domain.

Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 drivers/iommu/dma-iommu.c | 18 ++++++++++++++++--
 include/linux/iommu.h     |  4 ++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 7b1dfa0665df6..05e04934a5f81 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1799,6 +1799,20 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
 	return NULL;
 }
 
+/*
+ * Nested domains may not have an MSI cookie or accept mappings, but they may
+ * be related to a domain which does, so we let them tell us what they need.
+ */
+static struct iommu_domain *iommu_dma_get_msi_mapping_domain(struct device *dev)
+{
+	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
+
+	if (domain && domain->type == IOMMU_DOMAIN_NESTED &&
+	    domain->ops->get_msi_mapping_domain)
+		domain = domain->ops->get_msi_mapping_domain(domain);
+	return domain;
+}
+
 /**
  * iommu_dma_prepare_msi() - Map the MSI page in the IOMMU domain
  * @desc: MSI descriptor, will store the MSI page
@@ -1809,7 +1823,7 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
 int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
 {
 	struct device *dev = msi_desc_to_dev(desc);
-	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
+	struct iommu_domain *domain = iommu_dma_get_msi_mapping_domain(dev);
 	struct iommu_dma_msi_page *msi_page;
 	static DEFINE_MUTEX(msi_prepare_lock); /* see below */
 
@@ -1842,7 +1856,7 @@ int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
 void iommu_dma_compose_msi_msg(struct msi_desc *desc, struct msi_msg *msg)
 {
 	struct device *dev = msi_desc_to_dev(desc);
-	const struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
+	const struct iommu_domain *domain = iommu_dma_get_msi_mapping_domain(dev);
 	const struct iommu_dma_msi_page *msi_page;
 
 	msi_page = msi_desc_get_iommu_cookie(desc);
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 4d47f2c333118..69ed76f9c3ec4 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -638,6 +638,8 @@ struct iommu_ops {
  * @enable_nesting: Enable nesting
  * @set_pgtable_quirks: Set io page table quirks (IO_PGTABLE_QUIRK_*)
  * @free: Release the domain after use.
+ * @get_msi_mapping_domain: Return the related iommu_domain that should hold the
+ *                          MSI cookie and accept mapping(s).
  */
 struct iommu_domain_ops {
 	int (*attach_dev)(struct iommu_domain *domain, struct device *dev);
@@ -668,6 +670,8 @@ struct iommu_domain_ops {
 				  unsigned long quirks);
 
 	void (*free)(struct iommu_domain *domain);
+	struct iommu_domain *
+		(*get_msi_mapping_domain)(struct iommu_domain *domain);
 };
 
 /**
-- 
2.43.0