Documentation: s390-diag.rst: Make diag500 a generic KVM hypercall

Let's make it a generic KVM hypercall, allowing other subfunctions to
be more independent of virtio.

While at it, document that unsupported/unimplemented subfunctions result
in a SPECIFICATION exception.

This is a preparation for documenting a new subfunction.

Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Tested-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20241025141453.1210600-2-david@redhat.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/Documentation/virt/kvm/s390/s390-diag.rst b/Documentation/virt/kvm/s390/s390-diag.rst
index ca85f030eb0ba9f2b83b6dc5b4f90ebbc09d8314..48a326d41cc0196a924be3de743cd54bb49e1889 100644 (file)
--- a/Documentation/virt/kvm/s390/s390-diag.rst
+++ b/Documentation/virt/kvm/s390/s390-diag.rst
@@ -35,20 +35,24 @@ DIAGNOSE function codes not specific to KVM, please refer to the
 documentation for the s390 hypervisors defining them.
 
 
-DIAGNOSE function code 'X'500' - KVM virtio functions
------------------------------------------------------
+DIAGNOSE function code 'X'500' - KVM functions
+----------------------------------------------
 
-If the function code specifies 0x500, various virtio-related functions
-are performed.
+If the function code specifies 0x500, various KVM-specific functions
+are performed, including virtio functions.
 
-General register 1 contains the virtio subfunction code. Supported
-virtio subfunctions depend on KVM's userspace. Generally, userspace
-provides either s390-virtio (subcodes 0-2) or virtio-ccw (subcode 3).
+General register 1 contains the subfunction code. Supported subfunctions
+depend on KVM's userspace. Regarding virtio subfunctions, generally
+userspace provides either s390-virtio (subcodes 0-2) or virtio-ccw
+(subcode 3).
 
 Upon completion of the DIAGNOSE instruction, general register 2 contains
 the function's return code, which is either a return code or a subcode
 specific value.
 
+If the specified subfunction is not supported, a SPECIFICATION exception
+will be triggered.
+
 Subcode 0 - s390-virtio notification and early console printk
     Handled by userspace.