KVM: s390/cmm: Fix prefix handling for diag 10 balloon
KVM: s390/cmm: Fix prefix handling for diag 10 balloon

The old handling of prefix pages was broken in the diag10 ballooner.
We now rely on gmap_discard to check for start > end and do a
slow path if the prefix swap pages are affected:
1. discard the pages from start to prefix
2. discard the absolute 0 pages
3. discard the pages after prefix swap to end

Signed-off-by: Christian Borntraeger <49712f635b03c16d7f4c43df70e49ec8c565813d@de.ibm.com>
Reviewed-by: Thomas Huth <9e65be74847981e55b2564b6266c57d86d3bac05@linux.vnet.ibm.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs