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Re: [PATCH v1 6/9] s390x: kvm: topology: interception of PTF instruction


From: Pierre Morel
Subject: Re: [PATCH v1 6/9] s390x: kvm: topology: interception of PTF instruction
Date: Fri, 16 Jul 2021 13:23:27 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0



On 7/16/21 11:22 AM, Cornelia Huck wrote:
On Wed, Jul 14 2021, Pierre Morel <pmorel@linux.ibm.com> wrote:

Interception of the PTF instruction depending on the new
KVM_CAP_S390_CPU_TOPOLOGY KVM extension.

Wasn't that the capability that you dropped?

yes,


Is PTF supposed to be always intercepting? If that isn't configurable,
wouldn't older QEMUs generate exceptions for it? I'm a bit confused.

Yes, PTF generated an OPERATION exception on old QEMU, but was not used by the guest if it has not the topology facility 11.

So just as for STSI, I think we need the KVM_CAP_S390_CPU_TOPOLOGY I dropped because otherwise, now that the kernel will advertise facility 11, the guest will use it and it will get the exception that it should not get.

Regards,
Pierre



A global value is used to remember if a Topology change occured since
the last interception of a PTF instruction with function code 0.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
  hw/s390x/cpu-topology.c            | 19 +++++++++++
  include/hw/s390x/cpu-topology.h    |  8 +++++
  include/hw/s390x/s390-virtio-ccw.h |  1 +
  target/s390x/cpu.c                 |  4 +++
  target/s390x/cpu.h                 |  1 +
  target/s390x/kvm/kvm.c             | 52 ++++++++++++++++++++++++++++++
  6 files changed, 85 insertions(+)


--
Pierre Morel
IBM Lab Boeblingen



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