Re: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged_domain helper

[Robin Murphy <robin.murphy@arm.com>]

On 16/03/2023 1:21 am, Nicolin Chen wrote:
> Hi Robin,
> 
> How do you think about Jason's proposal below? I'd like to see
> us come to an agreement on an acceptable solution...

I think it's so thoroughly broken that I suspect Cunningham's law might
be at play, but fine, you win :) Hopefully it's sufficiently obvious how
the other pieces would fit around the patch below. FWIW I'd still prefer
a generic domain->s2_domain pointer rather than any op at all, but I'm
happy enough with this compromise.

Thanks,
Robin.

----->8-----
Subject: [PATCH] iommu/dma: Support MSIs through nested domains

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@arm.com>
---
  drivers/iommu/dma-iommu.c | 18 ++++++++++++++++--
  1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 99b2646cb5c7..66b0d5fa49f8 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1642,6 +1642,20 @@ 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
@@ -1652,7 +1666,7 @@ 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 */
  
@@ -1685,7 +1699,7 @@ 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);
-- 
2.39.2.101.g768bb238c484.dirty