Re: [PATCH v1 1/8] iommu: Add iommu_group_replace_domain()

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On 1/7/22 1:06 AM, Jason Gunthorpe wrote:
On Thu, Jan 06, 2022 at 10:20:46AM +0800, Lu Baolu wrote:
Expose an interface to replace the domain of an iommu group for frameworks
like vfio which claims the ownership of the whole iommu group.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
  include/linux/iommu.h | 10 ++++++++++
  drivers/iommu/iommu.c | 37 +++++++++++++++++++++++++++++++++++++
  2 files changed, 47 insertions(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 408a6d2b3034..66ebce3d1e11 100644
+++ b/include/linux/iommu.h
@@ -677,6 +677,9 @@ void iommu_device_unuse_dma_api(struct device *dev);
  int iommu_group_set_dma_owner(struct iommu_group *group, void *owner);
  void iommu_group_release_dma_owner(struct iommu_group *group);
  bool iommu_group_dma_owner_claimed(struct iommu_group *group);
+int iommu_group_replace_domain(struct iommu_group *group,
+			       struct iommu_domain *old,
+			       struct iommu_domain *new);
#else /* CONFIG_IOMMU_API */ @@ -1090,6 +1093,13 @@ static inline bool iommu_group_dma_owner_claimed(struct iommu_group *group)
  {
  	return false;
  }
+
+static inline int
+iommu_group_replace_domain(struct iommu_group *group, struct iommu_domain *old,
+			   struct iommu_domain *new)
+{
+	return -ENODEV;
+}
  #endif /* CONFIG_IOMMU_API */
/**
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 72a95dea688e..ab8ab95969f5 100644
+++ b/drivers/iommu/iommu.c
@@ -3431,3 +3431,40 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group)
  	return user;
  }
  EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
+
+/**
+ * iommu_group_replace_domain() - Replace group's domain
+ * @group: The group.
+ * @old: The previous attached domain. NULL for none.
+ * @new: The new domain about to be attached.
+ *
+ * This is to support backward compatibility for vfio which manages the dma
+ * ownership in iommu_group level.

This should mention it can only be used with iommu_group_set_dma_owner()

Sure.


+	if (old)
+		__iommu_detach_group(old, group);
+
+	if (new) {
+		ret = __iommu_attach_group(new, group);
+		if (ret && old)
+			__iommu_attach_group(old, group);
+	}

The sketchy error unwind here gives me some pause for sure. Maybe we
should define that on error this leaves the domain as NULL

Complicates vfio a tiny bit to cope with this failure but seems
cleaner than leaving it indeterminate.

Fair enough.


Jason


Best regards,
baolu



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