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

[Cornelia Huck]

On Fri,  4 Dec 2020 16:44:14 +1100
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 securable guest memory 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.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  hw/core/machine.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>