[PATCH] iommu: Fix deferred domain attachment

Joerg Roedel joro at 8bytes.org
Tue May 19 13:03:40 UTC 2020

From: Joerg Roedel <jroedel at suse.de>

The IOMMU core code has support for deferring the attachment of a domain
to a device. This is needed in kdump kernels where the new domain must
not be attached to a device before the device driver takes it over.

When the AMD IOMMU driver got converted to use the dma-iommu
implementation, the deferred attaching got lost. The code in
dma-iommu.c has support for deferred attaching, but it calls into
iommu_attach_device() to actually do it. But iommu_attach_device()
will check if the device should be deferred in it code-path and do
nothing, breaking deferred attachment.

Move the is_deferred_attach() check out of the attach_device path and
into iommu_group_add_device() to make deferred attaching work from the
dma-iommu code.

Cc: Jerry Snitselaar <jsnitsel at redhat.com>
Cc: Tom Murphy <murphyt7 at tcd.ie>
Cc: Robin Murphy <robin.murphy at arm.com>
Reported-by: Jerry Snitselaar <jsnitsel at redhat.com>
Suggested-by: Robin Murphy <robin.murphy at arm.com>
Tested-by: Jerry Snitselaar <jsnitsel at redhat.com>
Fixes: 795bbbb9b6f8 ("iommu/dma-iommu: Handle deferred devices")
Signed-off-by: Joerg Roedel <jroedel at suse.de>
 drivers/iommu/iommu.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 4050569188be..629d209b8e88 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -769,6 +769,15 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
 	return ret;
+static bool iommu_is_attach_deferred(struct iommu_domain *domain,
+				     struct device *dev)
+	if (domain->ops->is_attach_deferred)
+		return domain->ops->is_attach_deferred(domain, dev);
+	return false;
  * iommu_group_add_device - add a device to an iommu group
  * @group: the group into which to add the device (reference should be held)
@@ -821,7 +830,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
 	list_add_tail(&device->list, &group->devices);
-	if (group->domain)
+	if (group->domain  && !iommu_is_attach_deferred(group->domain, dev))
 		ret = __iommu_attach_device(group->domain, dev);
 	if (ret)
@@ -1893,9 +1902,6 @@ static int __iommu_attach_device(struct iommu_domain *domain,
 				 struct device *dev)
 	int ret;
-	if ((domain->ops->is_attach_deferred != NULL) &&
-	    domain->ops->is_attach_deferred(domain, dev))
-		return 0;
 	if (unlikely(domain->ops->attach_dev == NULL))
 		return -ENODEV;
@@ -1967,8 +1973,7 @@ EXPORT_SYMBOL_GPL(iommu_sva_unbind_gpasid);
 static void __iommu_detach_device(struct iommu_domain *domain,
 				  struct device *dev)
-	if ((domain->ops->is_attach_deferred != NULL) &&
-	    domain->ops->is_attach_deferred(domain, dev))
+	if (iommu_is_attach_deferred(domain, dev))
 	if (unlikely(domain->ops->detach_dev == NULL))

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