On 12/9/22 14:32, Thomas Huth wrote:
On 08/12/2022 10.44, Pierre Morel wrote:
Hi,
Implementation discussions
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CPU models
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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
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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.