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SubjectRe: [PATCH v4 15/32] vfio: introduce KVM-owned IOMMU type
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On 3/15/22 1:25 PM, Jason Gunthorpe wrote:
> On Tue, Mar 15, 2022 at 12:29:02PM -0400, Matthew Rosato wrote:
>> On 3/15/22 10:38 AM, Jason Gunthorpe wrote:
>>> On Tue, Mar 15, 2022 at 09:49:01AM -0400, Matthew Rosato wrote:
>>>
>>>> The rationale for splitting steps 1 and 2 are that VFIO_SET_IOMMU doesn't
>>>> have a mechanism for specifying more than the type as an arg, no? Otherwise
>>>> yes, you could specify a kvm fd at this point and it would have some other
>>>> advantages (e.g. skip notifier). But we still can't use the IOMMU for
>>>> mapping until step 3.
>>>
>>> Stuff like this is why I'd be much happier if this could join our
>>> iommfd project so we can have clean modeling of the multiple iommu_domains.
>>>
>>
>> I'd certainly be willing to collaborate so feel free to loop me in on the
>> discussions;
>
> Sure, I have you on my list. I've been waiting for Eric to get a bit
> further along on his ARM work so you have something appropriate to
> look at.
>
> In the mean time you can certainly work out the driver details as
> you've been doing here and hacking through VFIO. The iommu_domain
> logic is the big work item in this series, not the integration with
> the uAPI.
>

A subset of this series (enabling some s390x firmware-assist facilities)
is not tied to the iommu and would still provide value while continuing
to use vfio_iommu_type1 for all mapping -- so I think I'll look into a
next version that shrinks down to that subset (+ re-visit the setup API).

Separate from that, I will continue looking at implementing the nested
iommu_domain logic for s390, and continue to hack through VFIO for now.
I'll use an RFC series when I have something more to look at, likely
starting with the fully-pinned guest as you suggest; ultimately I'm
interested in both scenarios (pinned kvm guest & dynamic pinning during
shadow)

Thanks,
Matt

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