KVM: Fix dirty bit tracking for slots with large pages

(cherry picked from commit e244584f

)

When slot is already allocated and being asked to be tracked we need
to break the large pages.

This code flush the mmu when someone ask a slot to start dirty bit
tracking.
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

virt/kvm/kvm_main.c

@@ -550,6 +550,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		if (!new.dirty_bitmap)
 			goto out_free;
 		memset(new.dirty_bitmap, 0, dirty_bytes);
+		if (old.npages)
+			kvm_arch_flush_shadow(kvm);
 	}
 #endif /* not defined CONFIG_S390 */