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
> is
> > + * 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_prev_domain:
> > + /*
> > + * 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.
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 will
> 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.
Regards,
Sai
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