On 07/30/2018 01:15 PM, Pierre Morel wrote:
On 30/07/2018 11:24, David Hildenbrand wrote:
On 26.07.2018 21:54, Christian Borntraeger wrote:
From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
Introduces two new KVM interface to lear the APM, AQM and ADM masks in
the guest's CRYCB. The VCPUs are taken out of SIE to ensure the VCPUs do
not get out of synch.
s/synch/sync/
When will this be called and why?
If I read correctly, this can happen while other VCPUs are running
(currently in the SIE). Please note that
kvm_s390_vcpu_block_all/kvm_s390_vcpu_unblock_all will not care about
vSIE. So a CPU inside the vSIE loop will not be hindered of executing
the SIE. (because so far, all VCPU requests we handle don't rely on that)
So it could happen here, that after this call a vSIE CPU still can
access some adapters if we allowed to forward some of them to the nested
guest.
You are right for the principle.
However this function is only called when the mediated device is release
which is, as we do not support hotplug, when the vfio-device is closed
and the guest already disappeared.
So I do not think it is useful the way it is currently used.
What about just letting this call and function fall and take more
time on this problem when we introduce hotplug?
The point is, I don't think we can prohibit userspace to close the
vfio device before the VM is teared down (hot-unplug). The idea
was, do the best we can to give up the resources. I was not aware
of the problems with the VSIE.
QEMU however does make sure there is no hot-unplug. So no user
can observe the problem.
Halil
