Re: [RFC] virtio-iommu version 0.4

[Jean-Philippe Brucker <jean-philippe.brucker@arm.com>]

On 04/08/17 19:19, Jean-Philippe Brucker wrote:
> Other extensions are in preparation. I won't detail them here because v0.4
> already is a lot to digest, but in short, building on top of PROBE:
> 
> * First, since the IOMMU is paravirtualized, the device can expose some
>   properties of the physical topology to the guest, and let it allocate
>   resources more efficiently. For example, when the virtio-iommu manages
>   both physical and emulated endpoints, with different underlying IOMMUs,
>   we now have a way to describe multiple page and block granularities,
>   instead of forcing the guest to use the most restricted one for all
>   endpoints. This will most likely be in v0.5.

In order to extend requests with PASIDs and (later) nested mode, I intend
to rename "address_space" field to "domain", since it is a lot more
precise about what the field is referring to and the current name would
make these extensions confusing. Please find the rationale at [1].
"ioasid_bits" will be "domain_bits" and "VIRTIO_IOMMU_F_IOASID_BITS" will
be "VIRTIO_IOMMU_F_DOMAIN_BITS".

For those that had time to read this version, do you have other comments
and suggestions about v0.4? Otherwise it is the only update I have for
v0.5 (along with fine-grained address range and page size properties from
the quoted text) and I will send it soon.

In particular, please tell me now if you see the need for other
destructive changes like this one. They will be impossible to introduce
once a driver or device is upstream.

Thanks,
Jean

[1] https://www.spinics.net/lists/kvm/msg154573.html