Re: [PATCH v10 05/16] s390x: protvirt: Inhibit balloon when switching to protected mode

[Cornelia Huck]

On Wed, 18 Mar 2020 10:30:36 -0400
Janosch Frank <address@hidden> wrote:

> Ballooning in protected VMs can only be done when the guest shares the
> pages it gives to the host. If pages are not shared, the integrity
> checks will fail once those pages have been altered and are given back
> to the guest.
> 
> As we currently do not yet have a solution for this we will continue
> like this:
> 
> 1. We block ballooning now in QEMU (with this patch).
> 
> 2. Later we will provide a change to virtio that removes the blocker
> and adds VIRTIO_F_IOMMU_PLATFORM automatically by QEMU when doing the
> protvirt switch. This is OK, as the balloon driver in Linux (the only
> supported guest) will refuse to work with the IOMMU_PLATFORM feature
> bit set.
> 
> 3. Later, we can fix the guest balloon driver to accept the IOMMU
> feature bit and correctly exercise sharing and unsharing of balloon
> pages.
> 
> Signed-off-by: Janosch Frank <address@hidden>
> Reviewed-by: David Hildenbrand <address@hidden>
> Reviewed-by: Christian Borntraeger <address@hidden>
> Reviewed-by: Claudio Imbrenda <address@hidden>
> ---
>  hw/s390x/s390-virtio-ccw.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)

Reviewed-by: Cornelia Huck <address@hidden>