RFC: s390: extension capability for new address space layout

[Christian Borntraeger <borntraeger@de.ibm.com>]

Avi,Marcelo,

598841ca9919d008b520114d8a4378c4ce4e40a1 ([S390] use gmap address
spaces for kvm guest images) changed kvm on s390 to use a separate 
address space for kvm guests. We can now put KVM guests anywhere
in the user address mode with a size up to 8PB - as long as the 
memory is 1MB-aligned. This change was done without KVM extension
capability bit. 
The change was added after 3.0, but we still have a chance to add
a feature bit before 3.1 (keeping the releases in a sane state).

Can you have a look at the change below and give you ACK or NACK?
If ok, I would push this patch to Heiko to be submitted via the 
s390 stream for 3.1.

Christian

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -123,6 +123,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 
 	switch (ext) {
 	case KVM_CAP_S390_PSW:
+	case KVM_CAP_S390_GMAP:
 		r = 1;
 		break;
 	default:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 2c366b5..b2e9cc1 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -553,6 +553,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_SPAPR_TCE 63
 #define KVM_CAP_PPC_SMT 64
 #define KVM_CAP_PPC_RMA	65
+#define KVM_CAP_S390_GMAP 66
 
 #ifdef KVM_CAP_IRQ_ROUTING