Re: [PATCH 06/10] s390/cio: add basic protected virtualization support

Cornelia Huck
2019-05-16T13:54:44Z

On Thu, 16 May 2019 15:42:45 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Thu, 16 May 2019 08:32:28 +0200
> Cornelia Huck <cohuck@redhat.com> wrote:
>
> > On Wed, 15 May 2019 23:08:17 +0200
> > Halil Pasic <pasic@linux.ibm.com> wrote:
> >
> > > On Tue, 14 May 2019 10:47:34 -0400
> > > "Jason J. Herne" <jjherne@linux.ibm.com> wrote:
> >
> > > > Are we
> > > > worried that virtio data structures are going to be a burden on the 31-bit address space?
> > > >
> > > >
> > >
> > > That is a good question I can not answer. Since it is currently at least
> > > a page per queue (because we use dma direct, right Mimu?), I am concerned
> > > about this.
> > >
> > > Connie, what is your opinion?
> >
> > Yes, running into problems there was one of my motivations for my
> > question. I guess it depends on the number of devices and how many
> > queues they use. The problem is that it affects not only protected virt
> > guests, but all guests.
> >
>
> Unless things are about to change only devices that have
> VIRTIO_F_IOMMU_PLATFORM are affected. So it does not necessarily affect
> not protected virt guests. (With prot virt we have to use
> VIRTIO_F_IOMMU_PLATFORM.)
>
> If it were not like this, I would be much more worried.

If we go forward with this approach, documenting this side effect of
VIRTIO_F_IOMMU_PLATFORM is something that needs to happen.

>
> @Mimu: Could you please discuss this problem with the team? It might be
> worth considering to go back to the design of the RFC (i.e. cio/ccw stuff
> allocated from a common cio dma pool which gives you 31 bit addressable
> memory, and 64 bit dma mask for a ccw device of a virtio device).
>
> Regards,
> Halil
>