Re: [PATCH v7 04/15] s390x: protvirt: Inhibit balloon when switching to protected mode

[Janosch Frank]

On 3/9/20 2:42 PM, David Hildenbrand wrote:
> On 09.03.20 12:21, 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.
>>
>> Signed-off-by: Janosch Frank <address@hidden>
>> Reviewed-by: David Hildenbrand <address@hidden>
> 
> I think Christian requested to add the next steps.

Right, I lost that request somewhere.
This is what I have now:



s390x: protvirt: Inhibit balloon when switching to protected mode

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 guest balloon driver will reject to
work with the IOMMU change

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>

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