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

[Cornelia Huck]

On Tue, 8 Dec 2020 11:28:29 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> 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.

If you consider specifying the secure guest option as a way to tell
QEMU to make everything ready for running a secure guest, I'd certainly
consider it necessary. If you do not want to force it, you should not
do the secure guest preparation setup.

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