Re: [PATCH kernel] powerpc/iommu: Add iommu_ops to report capabilities and allow blocking domains

On 10/07/2022 16:29, Jason Gunthorpe wrote:
> On Sat, Jul 09, 2022 at 12:58:00PM +1000, Alexey Kardashevskiy wrote:
>   
>> driver->ops->attach_group on POWER attaches a group so VFIO claims ownership
>> over a group, not devices. Underlying API (pnv_ioda2_take_ownership()) does
>> not need to keep track of the state, it is one group, one ownership
>> transfer, easy.
> 
> It should not change, I think you can just map the attach_dev to the group?

There are multiple devices in a group, cannot just map 1:1.


>> What is exactly the reason why iommu_group_claim_dma_owner() cannot stay
>> inside Type1 (sorry if it was explained, I could have missed)?
> 
> It has nothing to do with type1 - the ownership system is designed to
> exclude other in-kernel drivers from using the group at the same time
> vfio is using the group. power still needs this protection regardless
> of if is using the formal iommu api or not.

POWER deals with it in vfio_iommu_driver_ops::attach_group.

>> Also, from another mail, you said iommu_alloc_default_domain() should fail
>> on power but at least IOMMU_DOMAIN_BLOCKED must be supported, or the whole
>> iommu_group_claim_dma_owner() thing falls apart.
> 
> Yes
> 
>> And iommu_ops::domain_alloc() is not told if it is asked to create a default
>> domain, it only takes a type.
> 
> "default domain" refers to the default type pased to domain_alloc(),
> it will never be blocking, so it will always fail on power.
> "default domain" is better understood as the domain used by the DMA
> API

The DMA API on POWER does not use iommu_ops, it is dma_iommu_ops from 
arch/powerpc/kernel/dma-iommu.c from before 2005. so the default domain 
is type = 0 where 0 = BLOCKED.


-- 
Alexey