KVM: s390: Add optional storage key checking to MEMOP IOCTL

KVM: s390: Add optional storage key checking to MEMOP IOCTL

User space needs a mechanism to perform key checked accesses when
emulating instructions.

The key can be passed as an additional argument.
Having an additional argument is flexible, as user space can
pass the guest PSW's key, in order to make an access the same way the
CPU would, or pass another key if necessary.

Signed-off-by: Janis Schoetterl-Glausch <[email protected]>
Reviewed-by: Claudio Imbrenda <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Reviewed-by: Janosch Frank <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Borntraeger <[email protected]>