All skey functions call skey_check_enable at their start, which checks
if we are in the PSTATE and injects a privileged operation exception
if we are.

Unfortunately they continue processing afterwards and perform the
operation anyhow as skey_check_enable does not deliver an error if the
exception injection was successful.

Let's move the PSTATE check into the skey functions and exit them on
such an occasion, also we now do not enable skey handling anymore in
such a case.
Signed-off-by: NJanosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Fixes: a7e19ab5 ("KVM: s390: handle missing storage-key facility")
Cc: <stable@vger.kernel.org> # v4.8+
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>