[Virtio-fs] virtiofs: Support for SEV encrypted guests

[Dr. David Alan Gilbert]

* Jim Cadden (jcadden at linux.vnet.ibm.com) wrote:
> Do you know if virtio-fs can support SEV encrypted guests?
> 
> I work on a project adding SEV support into kata containers. So far, we've
> been unable to boot SEV guests
> with kata's virtio-fs option (and use virtio-9p instead):
> 
> May 19 16:52:05 sev1 virtiofsd[74904]: [ID: 00074904] virtio_session_mount:
> Received vhost-user socket connection
> May 19 16:52:05 sev1 virtiofsd[74914]: [ID: 00000001] virtio_loop: Entry
> ...
> May 19 16:52:07 sev1 virtiofsd[74914]: [ID: 00000001] virtio_loop: Got VU
> event
> May 19 16:52:07 sev1 virtiofsd[74914]: [ID: 00000001] fv_panic:
> libvhost-user: Invalid vring_addr message
> 
> I know that other virtio devices use iommu and DMA apis to share
> non-encrypted pages between the host
> and encrypted guest. Could something similar be done with virtiofsd andthe
> virtio-fs virtio device?

I guess if you can guarantee that everything is going through
non-encrypted pages with the iommu, there shouldn't be a difference?
My only other worry is whether SEV works with a shared-memory backing
(e.g. /dev/shm or memfd with mmap shared).

I know there's an existing bug saying that virtio-fs doesn't work with
viommu:
https://bugzilla.redhat.com/show_bug.cgi?id=1812886

so I suspect it's fall out from that;  I think we just haven't
implemented the iommu compat code in the daemon.

> There are reported problems with vhost-user and SEV:
> https://bugzilla.redhat.com/show_bug.cgi?id=1797058

Yes, although it wasn't clear if that was just a performance problem or
not.

Dave

> Thanks for any insight,
> Jim
> 
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-- 
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK