diff options
authorRoger Pau Monne <roger.pau@citrix.com>2013-08-12 12:53:44 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-07 13:25:37 -0700
commitba4abe2e7f32f6d7fe3d92eeb4b1748c10b5f601 (patch)
parent46c0326164c98e556c35c3eb240273595d43425d (diff)
xen-blkfront: revoke foreign access for grants not mapped by the backend
commit fbe363c476afe8ec992d3baf682670a4bd1b6ce6 upstream. There's no need to keep the foreign access in a grant if it is not persistently mapped by the backend. This allows us to free grants that are not mapped by the backend, thus preventing blkfront from hoarding all grants. The main effect of this is that blkfront will only persistently map the same grants as the backend, and it will always try to use grants that are already mapped by the backend. Also the number of persistent grants in blkfront is the same as in blkback (and is controlled by the value in blkback). Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> Reviewed-by: David Vrabel <david.vrabel@citrix.com> Acked-by: Matt Wilson <msw@amazon.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 21 insertions, 3 deletions
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 1735b0d17e2..cbd9f6b910a 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -894,9 +894,27 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
/* Add the persistent grant into the list of free grants */
- for (i = 0; i < s->req.u.rw.nr_segments; i++) {
- list_add(&s->grants_used[i]->node, &info->persistent_gnts);
- info->persistent_gnts_c++;
+ for (i = 0; i < nseg; i++) {
+ if (gnttab_query_foreign_access(s->grants_used[i]->gref)) {
+ /*
+ * If the grant is still mapped by the backend (the
+ * backend has chosen to make this grant persistent)
+ * we add it at the head of the list, so it will be
+ * reused first.
+ */
+ list_add(&s->grants_used[i]->node, &info->persistent_gnts);
+ info->persistent_gnts_c++;
+ } else {
+ /*
+ * If the grant is not mapped by the backend we end the
+ * foreign access and add it to the tail of the list,
+ * so it will not be picked again unless we run out of
+ * persistent grants.
+ */
+ gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL);
+ s->grants_used[i]->gref = GRANT_INVALID_REF;
+ list_add_tail(&s->grants_used[i]->node, &info->persistent_gnts);
+ }