Re: [PATCH v6 06/18] s390x: protvirt: Inhibit balloon when switching to protected mode

[Christian Borntraeger]

On 04.03.20 12:42, Janosch Frank 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.
> 
> Hence, until we have a solution for this in the guest kernel, we
> inhibit ballooning when switching into protected mode and reverse that
> once we move out of it.

Can you maybe add the roadmap how to enable things.

1. we block ballooning now in QEMU (take this patch now)
2. Later Halil 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 guest balloon driver will reject to work with the IOMMU change
3. later we can fix the guest balloon driver to accept the IOMMU thing and then
do the right thing (make shared).

With an updated patch description:

Reviewed-by: Christian Borntraeger <address@hidden>


> 
> Signed-off-by: Janosch Frank <address@hidden>
> Reviewed-by: David Hildenbrand <address@hidden>
> ---
>  hw/s390x/s390-virtio-ccw.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 038bad54cd..b039178004 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -41,6 +41,7 @@
>  #include "hw/qdev-properties.h"
>  #include "hw/s390x/tod.h"
>  #include "sysemu/sysemu.h"
> +#include "sysemu/balloon.h"
>  #include "hw/s390x/pv.h"
>  #include <linux/kvm.h>
>  #include "migration/blocker.h"
> @@ -335,6 +336,7 @@ static void s390_machine_unprotect(S390CcwMachineState 
> *ms)
>          ms->pv = false;
>      }
>      migrate_del_blocker(pv_mig_blocker);
> +    qemu_balloon_inhibit(false);
>  }
>  
>  static int s390_machine_protect(S390CcwMachineState *ms)
> @@ -343,6 +345,7 @@ static int s390_machine_protect(S390CcwMachineState *ms)
>      CPUState *t;
>      int rc = -1;
>  
> +    qemu_balloon_inhibit(true);
>      if (!pv_mig_blocker) {
>          error_setg(&pv_mig_blocker,
>                     "protected VMs are currently not migrateable.");
>