Re: [PATCH 18/20] iommu: Add ops->domain_alloc_paging()

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Wed, 2023-05-03 at 16:35 -0300, Jason Gunthorpe wrote:
> On Wed, May 03, 2023 at 06:17:58PM +0100, Robin Murphy wrote:
> > On 2023-05-01 19:03, Jason Gunthorpe wrote:
> > > 
---8<---
> 
> > > @@ -1940,7 +1944,11 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
> > >   	if (type == IOMMU_DOMAIN_IDENTITY && bus->iommu_ops->identity_domain)
> > >   		return bus->iommu_ops->identity_domain;
> > > -	domain = bus->iommu_ops->domain_alloc(type);
> > > +	if ((type == IOMMU_DOMAIN_UNMANAGED || type == IOMMU_DOMAIN_DMA) &&
> > 
> > Logically, "type & __IOMMU_DOMAIN_PAGING", otherwise we're already missing
> > IOMMU_DOMAIN_DMA_FQ. Except maybe that's deliberate? 
> 
> It is deliberate for now, if it included FQ it would cause a bunch of
> ARM64 drivers to switch to lazy mode. I'll add a comment.
> 
> I have drafted a followup series that removes all the
> DMA/DMA_FQ/UNMANAGED checks from the remaining 6 drivers. I did this
> by adding an op flag 'prefer to use FQ' and made the core code drive
> the FQ decision from ops.

Ah that sounds like it could fit very well with s390's need for an even
lazier flush mode to handle the virtualized IOMMU with slow IOTLB flush
case aka _SQ / single flush queue mode. When you have anything ready
give me a ping and I can rework my DMA conversion on top of this.