[PATCH 0/4] s390: Reintroduce support for DCACHE_WORD_ACCESS

[Heiko Carstens <hca@linux.ibm.com>]

Support for DCACHE_WORD_ACCESS was recently removed [1] since it caused
problems with the incomplete handling of secure storage access
exceptions. It looked like fixing the exception handler would be a larger
effort; therefore support for DCACHE_WORD_ACCESS was removed as a work
around.

Address the potential problems that exist with secure storage access
exceptions and add support for DCACHE_WORD_ACCESS again.

In particular address the following problems:

- Reading the guest variable storage area via the /proc/kcore interface
  results in short reads. Address this by using a VM_SPARSE area for the
  guest variable storage area. VM_SPARSE areas will be handled like
  memory holes (zeros will be read).

- Fix handling of secure storage access exceptions in vmalloc area.

- Remove folio handling for secure storage access exceptions to avoid
  potential data corruption.

[1] 37540b8c287f ("s390: Revert support for DCACHE_WORD_ACCESS")

Heiko Carstens (4):
  KVM: s390: pv: Use VM_SPARSE area for guest variable storage area
  s390/mm: Fix handling of secure storage access exceptions in vmalloc area
  s390/mm: Remove folio handling for secure storage access exceptions
  s390: Add support for DCACHE_WORD_ACCESS (again)

 arch/s390/Kconfig                      |  1 +
 arch/s390/include/asm/asm-extable.h    |  4 ++
 arch/s390/include/asm/uv.h             |  2 +
 arch/s390/include/asm/word-at-a-time.h | 22 ++++++++++
 arch/s390/kernel/uv.c                  | 59 ++++++++++++++++++++++++++
 arch/s390/kvm/pv.c                     |  6 +--
 arch/s390/mm/extable.c                 | 18 ++++++++
 arch/s390/mm/fault.c                   | 10 ++---
 8 files changed, 112 insertions(+), 10 deletions(-)

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2.53.0