On 9/4/19 11:09 AM, Prakhya, Sai Praneeth wrote:
Hi Joerg,

Thanks a lot! for the review. I highly appreciate for sparing your time to 
review the patch :)

On Tue, Aug 20, 2019 at 07:42:25PM -0700, Sai Praneeth Prakhya wrote:
+       /*
+        * iommu_domain_alloc() takes "struct bus_type" as an argument which
+        * a member in "struct device". Changing a group's default domain type
+        * deals at iommu_group level rather than device level and hence there
+        * is no straight forward way to get "bus_type" of an iommu_group that
+        * could be passed to iommu_domain_alloc(). So, instead of directly
+        * calling iommu_domain_alloc(), use iommu_ops from previous default
+        * domain.
+        */
+       if (!prev_domain || !prev_domain->ops ||
+           !prev_domain->ops->domain_alloc || !type)
+               return -EINVAL;

Hmm, this isn't really nice and clean, but I understand why you need it.

I agree.. It didn't look good for me either :(
But, I didn't find any other better solution.

I will think about a better way to get iommu_ops here.

Sure! That will be great!

+       /*
+        * Free the existing default domain and replace it with the newly
+        * created default domain. No need to set group->domain because
+        * __iommu_attach_group() already does it on success.
+        */
+       iommu_domain_free(prev_domain);
+       group->default_domain = new_domain;
+       return 0;

It isn't obvious to me from this patch, how to are the dma_ops updated when
the default domain changes between identity and dma?

Thanks for raising this.
For intel_iommu, dma_map_ops is defined at drivers/iommu/intel-iommu.c and
all the callbacks like alloc(), map_sg() and map_page(), check if the device 
needs DMA mapping or not
by calling iommu_need_mapping(). The callbacks inherently do the right thing 
based on the outcome.
So, essentially the dma_ops are same for dma/identity domain.

This isn't always true as we are considering per-device dma ops.

Best regards,

I just realized (sorry!) that other iommu drivers (Eg: AMD) doesn't do it the 
same way i.e. looks like the callbacks
aren't checking if the device needs a dma mapping or identity mapping.
I will take a look at other iommu drivers and will handle this in V2.

Please let me know if I missed something.

+       /* Check if any device in the group still has a driver binded to it */
+       if (iommu_group_for_each_dev(group, NULL, is_driver_binded)) {
+               pr_err("Active drivers exist for devices in the group\n");
+               return -EBUSY;
+       }

This is racy with device driver probing code. Unfortunatly there is no clean way
out of that either, locking all devices in the group and then do the re-attach 
introduce a lock-inversion with group->mutex. But please put a comment here
saying that this might race with device driver probing.

Sure! Makes sense. Will add it in V2.


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