KVM: s390: vsie: Fix nested guest memory shadowing

Fix _do_shadow_pte() to use the correct pointer (guest pte instead of
nested guest) to set up the new pte.

Add a check to return -EOPNOTSUPP if the mapping for the nested guest
is writeable but the same page in the guest is only read-only.

Fixes: e38c884 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

Author: Claudio Imbrenda

arch/s390/kvm/gaccess.c

@@ -1436,13 +1436,19 @@ static int _do_shadow_pte(struct gmap *sg, gpa_t raddr, union pte *ptep_h, union
 
 	if (!pgste_get_trylock(ptep_h, &pgste))
 		return -EAGAIN;
-	newpte = _pte(f->pfn, f->writable, !p, 0);
-	newpte.s.d |= ptep->s.d;
-	newpte.s.sd |= ptep->s.sd;
-	newpte.h.p &= ptep->h.p;
-	pgste = _gmap_ptep_xchg(sg->parent, ptep_h, newpte, pgste, f->gfn, false);
-	pgste.vsie_notif = 1;
+	newpte = _pte(f->pfn, f->writable, !p, ptep_h->s.s);
+	newpte.s.d |= ptep_h->s.d;
+	newpte.s.sd |= ptep_h->s.sd;
+	newpte.h.p &= ptep_h->h.p;
+	if (!newpte.h.p && !f->writable) {
+		rc = -EOPNOTSUPP;
+	} else {
+		pgste = _gmap_ptep_xchg(sg->parent, ptep_h, newpte, pgste, f->gfn, false);
+		pgste.vsie_notif = 1;
+	}
 	pgste_set_unlock(ptep_h, pgste);
+	if (rc)
+		return rc;
 
 	newpte = _pte(f->pfn, 0, !p, 0);
 	if (!pgste_get_trylock(ptep, &pgste))
@@ -1477,6 +1483,9 @@ static int _do_shadow_crste(struct gmap *sg, gpa_t raddr, union crste *host, uni
 		newcrste.h.p &= oldcrste.h.p;
 		newcrste.s.fc1.vsie_notif = 1;
 		newcrste.s.fc1.prefix_notif = oldcrste.s.fc1.prefix_notif;
+		newcrste.s.fc1.s = oldcrste.s.fc1.s;
+		if (!newcrste.h.p && !f->writable)
+			return -EOPNOTSUPP;
 	} while (!_gmap_crstep_xchg_atomic(sg->parent, host, oldcrste, newcrste, f->gfn, false));
 
 	newcrste = _crste_fc1(f->pfn, oldcrste.h.tt, 0, !p);