linux-kernel - Re: [PATCH v4 15/32] vfio: introduce KVM-owned IOMMU type

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Message-ID: <5a1c64ac-df10-fb66-ad6d-39adf786f32b@linux.ibm.com>
Date:   Tue, 15 Mar 2022 12:29:02 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...dia.com>, borntraeger@...ux.ibm.com
Cc:     linux-s390@...r.kernel.org, alex.williamson@...hat.com,
        cohuck@...hat.com, schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        pmorel@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, frankja@...ux.ibm.com, david@...hat.com,
        imbrenda@...ux.ibm.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, joro@...tes.org, will@...nel.org,
        pbonzini@...hat.com, corbet@....net, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 15/32] vfio: introduce KVM-owned IOMMU type

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; but I got the impression that iommufd is not close to 
ready (maybe I'm wrong?) -- if so I really don't want to completely 
delay this zPCI support behind it as it has a significant benefit for 
kvm guests on s390x :(