KVM: s390: Implement KVM_PRE_FAULT_MEMORY

Implement KVM_PRE_FAULT_MEMORY on s390, and update documentation and
selftests accordingly.

Faulted-in pages will be marked as accessed, unlike x86, otherwise they
will trigger a minor fault when accessed. Avoiding such faults is one of
the points of KVM_PRE_FAULT_MEMORY.

This series depends on some kvm/s390 functions that are slightly buggy
at the moment. Those functions are being fixed in a separate series.
Even without those fixes, this series is not buggy, it's just a bit
inefficient in some corner cases.

CCing x86 people due to changes in the documentation and the selftests
just for completeness, since the selftest has been acked already.

v2->v3:
* Fix typos
* Correctly indicate page size in gmap_handle_minor_crste_fault() also
  in case nothing needed to be done.
* Pick up and acked-by

v1->v2:
* Add the crste_region3 flag in struct guest_fault to keep track of the
  page size used to solve a fault.
* Rewrite the s390 version of kvm_arch_vcpu_pre_fault_memory() so it
  looks and behaves similarly to the x86 version. No more loops, better
  handling of hugepage mappings, and more correct error handling.
* Remove the assertion vcpu->run->exit_reason == KVM_EXIT_IO from the
  selftest, as it is redundant and x86-specific.

Claudio Imbrenda (5):
  KVM: s390: Track page size in struct guest_fault
  KVM: s390: Implement KVM_PRE_FAULT_MEMORY
  KVM: s390: Update KVM_PRE_FAULT_MEMORY API documentation
  KVM: selftests: Fix pre_fault_memory_test to run on s390
  KVM: selftests: Enable pre_fault_memory_test for s390

 Documentation/virt/kvm/api.rst                |  5 ++-
 arch/s390/kvm/Kconfig                         |  1 +
 arch/s390/kvm/dat.h                           |  1 +
 arch/s390/kvm/gmap.c                          |  2 +
 arch/s390/kvm/kvm-s390.c                      | 45 +++++++++++++++++++
 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 .../selftests/kvm/pre_fault_memory_test.c     |  7 +--
 7 files changed, 54 insertions(+), 8 deletions(-)

-- 
2.54.0