KVM: s390: vsie: fix race during shadow creation

In the Linux kernel, the following vulnerability has been resolved:

KVM: s390: vsie: fix race during shadow creation

Right now it is possible to see gmap->private being zero in

kvm_s390_vsie_gmap_notifier resulting in a crash. This is due to the

fact that we add gmap->private == kvm after creation:

static int acquire_gmap_shadow(struct kvm_vcpu *vcpu,

struct vsie_page *vsie_page)

{

[...]

gmap = gmap_shadow(vcpu->arch.gmap, asce, edat);

if (IS_ERR(gmap))

return PTR_ERR(gmap);

gmap->private = vcpu->kvm;

Let children inherit the private field of the parent.