On 12/12/22 10:07, Thomas Huth wrote:
On 12/12/2022 09.51, Pierre Morel wrote:
On 12/9/22 14:32, Thomas Huth wrote:
On 08/12/2022 10.44, Pierre Morel wrote:
Hi,
Implementation discussions
==========================
CPU models
----------
Since the S390_FEAT_CONFIGURATION_TOPOLOGY is already in the CPU model
for old QEMU we could not activate it as usual from KVM but needed
a KVM capability: KVM_CAP_S390_CPU_TOPOLOGY.
Checking and enabling this capability enables
S390_FEAT_CONFIGURATION_TOPOLOGY.
Migration
---------
Once the S390_FEAT_CONFIGURATION_TOPOLOGY is enabled in the source
host the STFL(11) is provided to the guest.
Since the feature is already in the CPU model of older QEMU,
a migration from a new QEMU enabling the topology to an old QEMU
will keep STFL(11) enabled making the guest get an exception for
illegal operation as soon as it uses the PTF instruction.
I now thought that it is not possible to enable "ctop" on older QEMUs
since the don't enable the KVM capability? ... or is it still somehow
possible? What did I miss?
Thomas
Enabling ctop with ctop=on on old QEMU is not possible, this is right.
But, if STFL(11) is enable in the source KVM by a new QEMU, I can see
that even with -ctop=off the STFL(11) is migrated to the destination.
Is this with the "host" CPU model or another one? And did you explicitly
specify "ctop=off" at the command line, or are you just using the
default setting by not specifying it?
With explicit cpumodel and using ctop=off like in
sudo /usr/local/bin/qemu-system-s390x_master \
-m 512M \
-enable-kvm -smp 4,sockets=4,cores=2,maxcpus=8 \
-cpu z14,ctop=off \
-machine s390-ccw-virtio-7.2,accel=kvm \
...
regards,
Pierre
--
Pierre Morel
IBM Lab Boeblingen
