Re: [Qemu-devel] [RFC PATCH 7/8] VFIO: Add new IOCTL for IOMMU TLB invalidate propagation

[Jean-Philippe Brucker]

On 17/07/17 23:45, Alex Williamson wrote:
[..]
>>>
>>> How does a user learn which model(s) are supported by the interface?
>>> How do they learn which ops are supported?  Perhaps a good use for one of 
>>> those
>>> flag bits in the outer data structure is "probe".  
>>
>> My initial plan to user fills it, if the underlying HW doesn't support the
>> model, it refuses to service it. User should get a failure and stop to use
>> it. But your suggestion to have a probe or kinds of query makes sense.
>> How about we add one more operation for such purpose? Besides the
>> supported model query, I'd like to add more. E.g the HW IOMMU capabilities.
> 
> We also have VFIO_IOMMU_GET_INFO where the structure can be extended
> for missing capabilities.  Depending on the capability you want to
> describe, this might be a better, existing interface for it.

It might become hairy when physical IOMMUs start supporting multiple
formats, or when we want to describe multiple page table formats in
addition to PASID tables. I was wondering if sysfs iommu_group would be
better suited for this kind of hardware description with variable-length
properties, but a new ioctl-based probing mechanism would work as well.

Other things that we'll want to describe are fault reporting capability
and PASID range, which would fit better in vfio_device_info.

Thanks,
Jean