Re: [PATCH 06/17] iommufd/hw_pagetable: Use domain_alloc_user op for domain allocation

[Nicolin Chen]

On Thu, Feb 09, 2023 at 02:36:49PM -0400, Jason Gunthorpe wrote:
> On Thu, Feb 09, 2023 at 12:59:58PM -0500, Matthew Rosato wrote:
> > really should highlight that).  Otherwise, conditionally calling
> > iommu_domain_alloc(dev->bus) when !ops->domain_alloc_user (instead
> > of returning -EOPNOTSUPP) seems to restore the prior functionality
> > for me.
> 
> Yes, that is right if the input user data is 0 length or full of 0s
> then we should call the normal driver function

Maybe I am wrong, yet I recall that doing ops->domain_alloc_user
without a fallback was intentional to rule out drivers that don't
support IOMMUFD?

To be backward-compatible and concern about SMMU, we can opt in
ops->domain_alloc_user upon availability and then add a fallback:

	if ((!ops || !ops->domain_alloc_user) && user_data) {
		rc = -EOPNOTSUPP;
		goto out_abort;
	}

	if (ops->domain_alloc_user)
		hwpt->domain = ops->domain_alloc_user(dev, NULL, NULL);
	else
		hwpt->domain = iommu_domain_alloc(dev->bus);
	if (!hwpt->domain) {
		rc = -ENOMEM;
		goto out_abort;
	}

Yet, even by doing so, this series having the PATCH 07/17 that
moves iopt_table_add_domain() would temporally break IOMMUFD on
ARM platforms, until we add the ops->domain_alloc_user to SMMU
drivers.

Thanks
Nic