Re: [RFC v2 18/18] guest memory protection: Alter virtio default properties for protected guests

[Halil Pasic]

On Fri, 5 Jun 2020 12:45:35 +0200
Cornelia Huck <cohuck@redhat.com> wrote:

> On Thu, 21 May 2020 13:43:04 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > The default behaviour for virtio devices is not to use the platforms normal
> > DMA paths, but instead to use the fact that it's running in a hypervisor
> > to directly access guest memory.  That doesn't work if the guest's memory
> > is protected from hypervisor access, such as with AMD's SEV or POWER's PEF.
> > 
> > So, if a guest memory protection mechanism is enabled, then apply the
> > iommu_platform=on option so it will go through normal DMA mechanisms.
> > Those will presumably have some way of marking memory as shared with the
> > hypervisor or hardware so that DMA will work.
> 
> cc: Halil, who had been looking at the interaction of virtio-ccw
> devices and s390 protected virt.
> 
> (IIRC, we wanted to try with a on/off/auto property for virtio-ccw?)

Thanks Connie! I will definitely look into this. And regarding
on/off/auto I will try to send out something today.

Regards,
Halil