KVM: s390/mm: Make pages accessible before destroying the guest

Before we destroy the secure configuration, we better make all
pages accessible again. This also happens during reboot, where we reboot
into a non-secure guest that then can go again into secure mode. As
this "new" secure guest will have a new ID we cannot reuse the old page
state.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>

arch/s390/include/asm/gmap.h

@@ -149,4 +149,5 @@ int gmap_mprotect_notify(struct gmap *, unsigned long start,
 void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long dirty_bitmap[4],
 			     unsigned long gaddr, unsigned long vmaddr);
 int gmap_mark_unmergeable(void);
+void s390_reset_acc(struct mm_struct *mm);
 #endif /* _ASM_S390_GMAP_H */

arch/s390/kvm/pv.c

@@ -140,6 +140,9 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
 {
 	int cc;
 
+	/* make all pages accessible before destroying the guest */
+	s390_reset_acc(kvm->mm);
+
 	cc = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
 			   UVC_CMD_DESTROY_SEC_CONF, rc, rrc);
 	WRITE_ONCE(kvm->arch.gmap->guest_handle, 0);

arch/s390/mm/gmap.c

@@ -2650,3 +2650,38 @@ void s390_reset_cmma(struct mm_struct *mm)
 	up_write(&mm->mmap_sem);
 }
 EXPORT_SYMBOL_GPL(s390_reset_cmma);
+
+/*
+ * make inaccessible pages accessible again
+ */
+static int __s390_reset_acc(pte_t *ptep, unsigned long addr,
+			    unsigned long next, struct mm_walk *walk)
+{
+	pte_t pte = READ_ONCE(*ptep);
+
+	if (pte_present(pte))
+		WARN_ON_ONCE(uv_convert_from_secure(pte_val(pte) & PAGE_MASK));
+	return 0;
+}
+
+static const struct mm_walk_ops reset_acc_walk_ops = {
+	.pte_entry		= __s390_reset_acc,
+};
+
+#include <linux/sched/mm.h>
+void s390_reset_acc(struct mm_struct *mm)
+{
+	/*
+	 * we might be called during
+	 * reset:                             we walk the pages and clear
+	 * close of all kvm file descriptors: we walk the pages and clear
+	 * exit of process on fd closure:     vma already gone, do nothing
+	 */
+	if (!mmget_not_zero(mm))
+		return;
+	down_read(&mm->mmap_sem);
+	walk_page_range(mm, 0, TASK_SIZE, &reset_acc_walk_ops, NULL);
+	up_read(&mm->mmap_sem);
+	mmput(mm);
+}
+EXPORT_SYMBOL_GPL(s390_reset_acc);