[SRU][J][I][F][PATCH 1/1] KVM: s390: vsie/gmap: reduce gmap_rmap overhead

[frank.heimes at canonical.com]

From: Christian Borntraeger <borntraeger at linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1974017

there are cases that trigger a 2nd shadow event for the same
vmaddr/raddr combination. (prefix changes, reboots, some known races)
This will increase memory usages and it will result in long latencies
when cleaning up, e.g. on shutdown. To avoid cases with a list that has
hundreds of identical raddrs we check existing entries at insert time.
As this measurably reduces the list length this will be faster than
traversing the list at shutdown time.

In the long run several places will be optimized to create less entries
and a shrinker might be necessary.

Fixes: 4be130a08420 ("s390/mm: add shadow gmap support")
Signed-off-by: Christian Borntraeger <borntraeger at linux.ibm.com>
Acked-by: David Hildenbrand <david at redhat.com>
Link: https://lore.kernel.org/r/20220429151526.1560-1-borntraeger@linux.ibm.com
Signed-off-by: Heiko Carstens <hca at linux.ibm.com>
(cherry picked from commit a06afe8383080c630a7a528b8382fc6bb4925b61)
Signed-off-by: Frank Heimes <frank.heimes at canonical.com>
---
 arch/s390/mm/gmap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index d63c0ccc5ccd..ce39bb3c4806 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -1183,6 +1183,7 @@ EXPORT_SYMBOL_GPL(gmap_read_table);
 static inline void gmap_insert_rmap(struct gmap *sg, unsigned long vmaddr,
 				    struct gmap_rmap *rmap)
 {
+	struct gmap_rmap *temp;
 	void __rcu **slot;
 
 	BUG_ON(!gmap_is_shadow(sg));
@@ -1190,6 +1191,12 @@ static inline void gmap_insert_rmap(struct gmap *sg, unsigned long vmaddr,
 	if (slot) {
 		rmap->next = radix_tree_deref_slot_protected(slot,
 							&sg->guest_table_lock);
+		for (temp = rmap->next; temp; temp = temp->next) {
+			if (temp->raddr == rmap->raddr) {
+				kfree(rmap);
+				return;
+			}
+		}
 		radix_tree_replace_slot(&sg->host_to_rmap, slot, rmap);
 	} else {
 		rmap->next = NULL;
-- 
2.25.1