[RFC PATCH v5 0/1] s390x: Improvements to SIGP handling [KVM]

[Eric Farman <farman@linux.ibm.com>]

Here is an update to the handling of SIGP between kernel and userspace.

As before, I'm looking at problems encountered when a SIGP order that is
processed in the kernel (for example, SIGP SENSE) is run concurrently
with another one is processed in userspace (for example, SIGP STOP).
Being able to provide an honest answer in the SIGP SENSE as to whether
the targeted VCPU is/not stopped is important to provide a consistent
answer while a guest OS is bringing its configuration online.

This version was suggested by David Hildenbrand on v3 [1], where we
examine the target vcpu for a pending STOP/RESTART IRQ while processing
a SIGP order in-kernel, and returning the CC2 if one is in-flight.

Unlike v2-v4 of this RFC, this solution requires no changes to userspace
to exploit a new interface, but a small change is made on the QEMU side
to keep the sequence of events in checks.

Thoughts?

[1] https://lore.kernel.org/r/858e4f2b-d601-a4f1-9e80-8f7838299c9a@redhat.com/

Previous RFCs:
v1: https://lore.kernel.org/r/20211008203112.1979843-1-farman@linux.ibm.com/
v2: https://lore.kernel.org/r/20211102194652.2685098-1-farman@linux.ibm.com/
v3: https://lore.kernel.org/r/20211110203322.1374925-1-farman@linux.ibm.com/
v4: https://lore.kernel.org/r/20211119213707.2363945-1-farman@linux.ibm.com/

Eric Farman (1):
  KVM: s390: Clarify SIGP orders versus STOP/RESTART

 arch/s390/kvm/interrupt.c |  7 +++++++
 arch/s390/kvm/kvm-s390.c  |  9 +++++++--
 arch/s390/kvm/kvm-s390.h  |  1 +
 arch/s390/kvm/sigp.c      | 28 ++++++++++++++++++++++++++++
 4 files changed, 43 insertions(+), 2 deletions(-)

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2.32.0