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s390/mm: limit number of real-space gmap shadows

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We have no known user of real-space designation and only support it to
be architecture compliant.

Gmap shadows with real-space designation are never unshadowed
automatically, as there is nothing to protect for the top level table.

So let's simply limit the number of such shadows to one by removing
existing ones on creation of another one.

Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
David Hildenbrand 2016-05-02 12:10:17 +02:00 committed by Christian Borntraeger
parent 3218f7094b
commit 717c05554a
1 changed files with 13 additions and 0 deletions
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13
arch/s390/mm/gmap.c
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@ -1455,6 +1455,19 @@ struct gmap *gmap_shadow(struct gmap *parent, unsigned long asce,
gmap_free(new);
return sg;
}
if (asce & _ASCE_REAL_SPACE) {
/* only allow one real-space gmap shadow */
list_for_each_entry(sg, &parent->children, list) {
if (sg->orig_asce & _ASCE_REAL_SPACE) {
spin_lock(&sg->guest_table_lock);
gmap_unshadow(sg);
spin_unlock(&sg->guest_table_lock);
list_del(&sg->list);
gmap_put(sg);
break;
}
}
}
atomic_set(&new->ref_count, 2);
list_add(&new->list, &parent->children);
if (asce & _ASCE_REAL_SPACE) {