Re: [for-6.0 v5 12/13] securable guest memory: Alter virtio default properties for protected guests

[Halil Pasic]

On Tue, 8 Dec 2020 12:54:03 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> > > >>> +         * Virtio devices can't count on directly accessing guest
> > > >>> +         * memory, so they need iommu_platform=on to use normal DMA
> > > >>> +         * mechanisms.  That requires also disabling legacy virtio
> > > >>> +         * support for those virtio pci devices which allow it.
> > > >>> +         */
> > > >>> +        object_register_sugar_prop(TYPE_VIRTIO_PCI, "disable-legacy",
> > > >>> +                                   "on", true);
> > > >>> +        object_register_sugar_prop(TYPE_VIRTIO_DEVICE, 
> > > >>> "iommu_platform",
> > > >>> +                                   "on", false);    
> > > >>
> > > >> I have not followed all the history (sorry). Should we also set 
> > > >> iommu_platform
> > > >> for virtio-ccw? Halil?
> > > >>  
> > > > 
> > > > That line should add iommu_platform for all virtio devices, shouldn't
> > > > it?  
> > > 
> > > Yes, sorry. Was misreading that with the line above. 
> > >   
> > 
> > I believe this is the best we can get. In a sense it is still a
> > pessimization,  
> 
> I'm not really clear on what you're getting at here.

By pessimiziation, I mean that we are going to indicate
_F_PLATFORM_ACCESS even if it isn't necessary, because the guest never
opted in for confidential/memory protection/memory encryption. We have
discussed this before, and I don't see a better solution that works for
everybody.

Regards,
Halil

pgpyn52QbfXSe.pgp
Description: OpenPGP digital signature