KVM: s390: add capability indicating COW support
Currently qemu/kvm on s390 uses a guest mapping that does not
allow the guest backing page table to be write-protected to
support older systems. On those older systems a host write
protection fault will be delivered to the guest.
Newer systems allow to write-protect the guest backing memory
and let the fault be delivered to the host, thus allowing COW.
Use a capability bit to tell qemu if that is possible.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/s390/include/asm/sclp.h b/arch/s390/include/asm/sclp.h
index fed7bee..bf238c5 100644
--- a/arch/s390/include/asm/sclp.h
+++ b/arch/s390/include/asm/sclp.h
@@ -48,6 +48,7 @@
void sclp_facilities_detect(void);
unsigned long long sclp_get_rnmax(void);
unsigned long long sclp_get_rzm(void);
+u8 sclp_get_fac85(void);
int sclp_sdias_blk_count(void);
int sclp_sdias_copy(void *dest, int blk_num, int nr_blks);
int sclp_chp_configure(struct chp_id chpid);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e5e3800..5c761bf 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -28,6 +28,7 @@
#include <asm/pgtable.h>
#include <asm/nmi.h>
#include <asm/switch_to.h>
+#include <asm/sclp.h>
#include "kvm-s390.h"
#include "gaccess.h"
@@ -140,6 +141,9 @@
case KVM_CAP_MAX_VCPUS:
r = KVM_MAX_VCPUS;
break;
+ case KVM_CAP_S390_COW:
+ r = sclp_get_fac85() & 0x2;
+ break;
default:
r = 0;
}