Re: [PATCH] iommu: Implement deferred domain attachment

[Joerg Roedel]

On Fri, May 15, 2020 at 04:42:23PM +0100, Robin Murphy wrote:
> >   struct iommu_domain *iommu_get_dma_domain(struct device *dev)
> >   {
> > -	return dev->iommu_group->default_domain;
> > +	struct iommu_domain *domain = dev->iommu_group->default_domain;
> > +
> > +	if (__iommu_is_attach_deferred(domain, dev))
> > +		__iommu_attach_device_no_defer(domain, dev);
> 
> This raises a red flag, since iommu-dma already has explicit deferred attach
> handling where it should need it, immediately after this is called to
> retrieve the domain. The whole thing smells to me like we should have an
> explicit special-case in iommu_probe_device() rather than hooking
> __iommu_attach_device() in general then having to bodge around the fallout
> elsewhere.

Good point, I missed that. But it didn't work for its only user, the
AMD IOMMU driver, the reason is that it calls iommu_attach_device(),
which in its code-path checks for deferred attaching again and bails
out, without do the real attachment.

But below updated fix should work. Jerry, could you please test it
again?