On Wed, 11 Mar 2020 09:21:40 -0400
Janosch Frank <fran...@linux.ibm.com> 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)
add trailing '.'
>
> 2. Later we will provide a change to virtio that removes the blocker
s/Later/Later,/
> 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
"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
"Later, we can fix the Linux guest balloon driver..."
> feature bit and correctly exercise sharing and unsharing of balloon
> pages
again, missing trailing '.'
>
> Signed-off-by: Janosch Frank <fran...@linux.ibm.com>
> Reviewed-by: David Hildenbrand <da...@redhat.com>
> Reviewed-by: Christian Borntraeger <borntrae...@de.ibm.com>
> ---
> hw/s390x/s390-virtio-ccw.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index deb31e060052d279..066e01f303c35671 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 "migration/blocker.h"
>
> @@ -326,6 +327,7 @@ static void s390_machine_unprotect(S390CcwMachineState
> *ms)
> ms->pv = false;
> migrate_del_blocker(pv_mig_blocker);
> error_free_or_abort(&pv_mig_blocker);
> + qemu_balloon_inhibit(false);
> }
>
> static int s390_machine_protect(S390CcwMachineState *ms)
> @@ -333,10 +335,12 @@ static int s390_machine_protect(S390CcwMachineState *ms)
> Error *local_err = NULL;
> int rc;
>
Maybe add a comment?
/*
* Ballooning on protected VMs needs support in the guest for
* sharing and unsharing balloon pages. Block ballooning for
* now, until we have a solution to make at least Linux guests
* either support it or fail gracefully.
*/
> + qemu_balloon_inhibit(true);
> error_setg(&pv_mig_blocker,
> "protected VMs are currently not migrateable.");
> rc = migrate_add_blocker(pv_mig_blocker, &local_err);
> if (local_err) {
> + qemu_balloon_inhibit(false);
> error_report_err(local_err);
> error_free_or_abort(&pv_mig_blocker);
> return rc;
> @@ -345,6 +349,7 @@ static int s390_machine_protect(S390CcwMachineState *ms)
> /* Create SE VM */
> rc = s390_pv_vm_enable();
> if (rc) {
> + qemu_balloon_inhibit(false);
> error_report_err(local_err);
> migrate_del_blocker(pv_mig_blocker);
> error_free_or_abort(&pv_mig_blocker);
