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SubjectRe: [RFC PATCH 11/34] iommu: Split off default domain allocation from group assignment
Hi Joerg,

On Tue, 2020-04-07 at 20:37 +0200, Joerg Roedel wrote:
> From: Joerg Roedel <>
> When a bus is initialized with iommu-ops, all devices on the bus are
> scanned and iommu-groups are allocated for them, and each groups will
> also get a default domain allocated.
> Until now this happened as soon as the group was created and the first
> device added to it. When other devices with different default domain
> requirements were added to the group later on, the default domain was
> re-allocated, if possible.
> This resulted in some back and forth and unnecessary allocations, so
> change the flow to defer default domain allocation until all devices
> have been added to their respective IOMMU groups.
> The default domains are allocated for newly allocated groups after
> each device on the bus is handled and was probed by the IOMMU driver.
> Signed-off-by: Joerg Roedel <>
> ---

I had to add the following for initial VMD support. The new PCIe domain
added on VMD endpoint probe didn't have the dev_iommu member set on the
VMD subdevices, which I'm guessing is due to probe_iommu_group already
having been run on the VMD endpoint's group prior to those subdevices
being added.

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 8a5e1ac328dd..ac1e4fb9bf48 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1577,6 +1577,9 @@ static int iommu_bus_notifier(struct notifier_block *nb,
if (action == BUS_NOTIFY_ADD_DEVICE) {
int ret;

+ if (!dev_iommu_get(dev))
+ return -ENOMEM;
ret = iommu_probe_device(dev);
return (ret) ? NOTIFY_DONE : NOTIFY_OK;
} else if (action == BUS_NOTIFY_REMOVED_DEVICE) {
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