[v11,0/3] s390x: KVM: CPU Topology

Message

Pierre Morel July 1, 2022, 4:25 p.m. UTC

Hi all,

This new spin suppress the check for real cpu migration and
modify the checking of valid function code inside the interception
of the STSI instruction.

The series provides:
0- Modification of the ipte lock handling to use KVM instead of the
   vcpu as an argument because ipte lock work on SCA which is uniq
   per KVM structure and common to all vCPUs.
1- interception of the STSI instruction forwarding the CPU topology
2- interpretation of the PTF instruction
3- a KVM capability for the userland hypervisor to ask KVM to 
   setup PTF interpretation.
4- KVM ioctl to get and set the MTCR bit of the SCA in order to
   migrate this bit during a migration.


0- Foreword

The S390 CPU topology is reported using two instructions:
- PTF, to get information if the CPU topology did change since last
  PTF instruction or a subsystem reset.
- STSI, to get the topology information, consisting of the topology
  of the CPU inside the sockets, of the sockets inside the books etc.

The PTF(2) instruction report a change if the STSI(15.1.2) instruction
will report a difference with the last STSI(15.1.2) instruction*.
With the SIE interpretation, the PTF(2) instruction will report a
change to the guest if the host sets the SCA.MTCR bit.

*The STSI(15.1.2) instruction reports:
- The cores address within a socket
- The polarization of the cores
- The CPU type of the cores
- If the cores are dedicated or not

We decided to implement the CPU topology for S390 in several steps:

- first we report CPU hotplug

In future development we will provide:

- modification of the CPU mask inside sockets
- handling of shared CPUs
- reporting of the CPU Type
- reporting of the polarization


1- Interception of STSI

To provide Topology information to the guest through the STSI
instruction, we forward STSI with Function Code 15 to the
userland hypervisor which will take care to provide the right
information to the guest.

To let the guest use both the PTF instruction  to check if a topology
change occurred and sthe STSI_15.x.x instruction we add a new KVM
capability to enable the topology facility.

2- Interpretation of PTF with FC(2)

The PTF instruction reports a topology change if there is any change
with a previous STSI(15.1.2) SYSIB.

Changes inside a STSI(15.1.2) SYSIB occur if CPU bits are set or clear
inside the CPU Topology List Entry CPU mask field, which happens with
changes in CPU polarization, dedication, CPU types and adding or
removing CPUs in a socket.

Considering that the KVM guests currently only supports:
- horizontal polarization
- type 3 (Linux) CPU

And that we decide to support only:
- dedicated CPUs on the host
- pinned vCPUs on the guest

the creation of vCPU will is the only trigger to set the MTCR bit for
a guest.

The reporting to the guest is done using the Multiprocessor
Topology-Change-Report (MTCR) bit of the utility entry of the guest's
SCA which will be cleared during the interpretation of PTF.

Regards,
Pierre

Pierre Morel (3):
  KVM: s390: Cleanup ipte lock access and SIIF facility checks
  KVM: s390: guest support for topology function
  KVM: s390: resetting the Topology-Change-Report

 Documentation/virt/kvm/api.rst   | 25 +++++++++
 arch/s390/include/asm/kvm_host.h | 18 +++++-
 arch/s390/include/uapi/asm/kvm.h | 10 ++++
 arch/s390/kvm/gaccess.c          | 96 ++++++++++++++++----------------
 arch/s390/kvm/gaccess.h          |  6 +-
 arch/s390/kvm/kvm-s390.c         | 89 +++++++++++++++++++++++++++++
 arch/s390/kvm/priv.c             | 22 +++++---
 arch/s390/kvm/vsie.c             |  8 +++
 include/uapi/linux/kvm.h         |  1 +
 9 files changed, 214 insertions(+), 61 deletions(-)