Re: [PATCH 20/20] iommu: Convert remaining simple drivers to domain_alloc_paging()

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, May 02, 2023 at 04:52:32PM +0200, Niklas Schnelle wrote:
> @@ -1947,7 +1948,7 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
>         if ((type == IOMMU_DOMAIN_UNMANAGED || type == IOMMU_DOMAIN_DMA) &&
>             bus->iommu_ops->domain_alloc_paging)
>                 domain = bus->iommu_ops->domain_alloc_paging(dev);
> -       else
> +       else if (bus->iommu_ops->domain_alloc)
>                 domain = bus->iommu_ops->domain_alloc(type);
>         if (!domain)
>                 return NULL;

Agh, yes, it should fail, this is right, I'll fold it in, thanks

> This then uses the fallback of an empty IOMMU_DOMAIN_UNMANAGED and I
> get a working device in the guest. Also tried hot unplug where the
> device is taken over by the host again.

Great, thanks, I'll add your tested-by for the s390 drivers.

> I think with my DMA API
> conversion patches we can support blocking domains properly but for a
> temporary solution the above may be acceptable.

Yes, this is a good idea, I encourage all drivers to implement at
least one of BLOCKING or IDENTITY as global static singletons that
can't fail - this will allow us to have cleaner error recovery flows.

Jason