From mboxrd@z Thu Jan  1 00:00:00 1970
From: Halil Pasic <pasic@linux.ibm.com>
Subject: Re: [PATCH 06/10] s390/cio: add basic protected virtualization support
Date: Thu, 16 May 2019 15:42:45 +0200
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To: Cornelia Huck <cohuck@redhat.com>
Cc: "Jason J. Herne" <jjherne@linux.ibm.com>, linux-s390@vger.kernel.org, Thomas Huth <thuth@redhat.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org, Sebastian Ott <sebott@linux.ibm.com>, "Michael S. Tsirkin" <mst@redhat.com>, Farhan Ali <alifm@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>, virtualization@lists.linux-foundation.org, Christoph Hellwig <hch@infradead.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Michael Mueller <mimu@linux.ibm.com>, Viktor Mihajlovski <mihajlov@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Janosch Frank <frankja@linux.ibm.com>
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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.

@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