Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces

Jean-Philippe Brucker
2018-05-24T15:04:39Z

On 24/05/18 12:50, Ilias Apalodimas wrote:
>> Interesting, I hadn't thought about this use-case before. At first I
>> thought you were talking about mdev devices assigned to VMs, but I think
>> you're referring to mdevs assigned to userspace drivers instead? Out of
>> curiosity, is it only theoretical or does someone actually need this?
>
> There has been some non upstreamed efforts to have mdev and produce userspace
> drivers. Huawei is using it on what they call "wrapdrive" for crypto devices and
> we did a proof of concept for ethernet interfaces. At the time we choose not to
> involve the IOMMU for the reason you mentioned, but having it there would be
> good.

I'm guessing there were good reasons to do it that way but I wonder, is
it not simpler to just have the kernel driver create a /dev/foo, with a
standard ioctl/mmap/poll interface? Here VFIO adds a layer of
indirection, and since the mediating driver has to implement these
operations already, what is gained?

Thanks,
Jean