Pull Xen block driver fixes from Konrad:
"Fix for flushing out persistent pages at a deterministic rate"
* 'stable/for-jens-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen:
xen/blkback: remove unused pers_gnts_lock from struct xen_blkif_ring
xen/blkback: move persistent grants flags to bool
xen/blkfront: reorder tests in xlblk_init()
xen/blkfront: cleanup stale persistent grants
xen/blkback: don't keep persistent grants too long
