s390/mm: allow to check if a gmap shadow is valid

It will be very helpful to have a mechanism to check without any locks
if a given gmap shadow is still valid and matches the given properties.

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>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 4a1434bc2f0e..d00e4abb559e 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -1408,6 +1408,26 @@ static struct gmap *gmap_find_shadow(struct gmap *parent, unsigned long asce,
 }
 
 /**
+ * gmap_shadow_valid - check if a shadow guest address space matches the
+ *                     given properties and is still valid
+ * @sg: pointer to the shadow guest address space structure
+ * @asce: ASCE for which the shadow table is requested
+ * @edat_level: edat level to be used for the shadow translation
+ *
+ * Returns 1 if the gmap shadow is still valid and matches the given
+ * properties, the caller can continue using it. Returns 0 otherwise, the
+ * caller has to request a new shadow gmap in this case.
+ *
+ */
+int gmap_shadow_valid(struct gmap *sg, unsigned long asce, int edat_level)
+{
+        if (sg->removed)
+                return 0;
+        return sg->orig_asce == asce && sg->edat_level == edat_level;
+}
+EXPORT_SYMBOL_GPL(gmap_shadow_valid);
+
+/**
  * gmap_shadow - create/find a shadow guest address space
  * @parent: pointer to the parent gmap
  * @asce: ASCE for which the shadow table is created