Re: [PATCH 0/7] iommu cleanup and refactoring

[Lu Baolu]

On 1/25/22 11:16 PM, Jason Gunthorpe wrote:
> On Tue, Jan 25, 2022 at 02:48:02PM +0000, Robin Murphy wrote:
>   
> > Agreed, certainly an IOMMU_DOMAIN_SVA type that can both encapsulate the mm
> > and effectively replace iommu_sva seems like a logical and fairly small next
> > step. We already have the paradigm of different domain types supporting
> > different ops, so initially an SVA domain would simply allow bind/unbind
> > rather than attach/detach/map/unmap.
>
> I hope we can quickly get to a PASID enabled generic attach/detach
> scheme - we really need this to do the uAPI part of this interface.

Agreed. Jacob is working on kernel DMA with PASID. He needs such
interfaces as well. I have worked out an implementation for vt-d driver.
It could be post for review inside Jacob's series for kernel DMA with
PASID.

> > they are fundamentally different things in their own right, and the ideal
> > API should give us the orthogonality to also bind a device to an SVA domain
> > without PASID (e.g. for KVM stage 2, or userspace assignment of simpler
> > fault/stall-tolerant devices), or attach PASIDs to regular iommu_domains.
>
> Yes, these are orthogonal things. A iommu driver that supports PASID
> ideally should support PASID enabled attach/detatch for every
> iommu_domain type it supports.
>
> SVA should not be entangled with PASID beyond that SVA is often used
> with PASID - a SVA iommu_domain should be fully usable with a RID too.

The prototype of PASID enabled attach/detach ops could look like:

       int (*attach_dev_pasid)(struct iommu_domain *domain,
                               struct device *dev, ioasid_t id);
       void (*detach_dev_pasid)(struct iommu_domain *domain,
                                struct device *dev, ioasid_t id);

But the iommu driver should implement different callbacks for

1) attaching an IOMMU DMA domain to a PASID on device;
   - kernel DMA with PASID
   - mdev-like device passthrough
   - etc.
2) attaching a CPU-shared domain to a PASID on device;
   - SVA
   - guest PASID
   - etc.

> I'm hoping to see the core iommu code provide some simplified "SVA"
> API that under the covers creates a SVA domain and then does a normal
> PASID attach using the global PASID in the mm_struct - the
> driver should not care what, or even if, PASID is used for a SVA
> domain.
>
> Jason

Best regards,
baolu