vfio: parallelize vfio_pin_map_dma

hulk inclusion
category: feature
bugzilla: 13228
CVE: NA
---------------------------

When starting a large-memory kvm guest, it takes an excessively long
time to start the boot process because qemu must pin all guest pages to
accommodate DMA when VFIO is in use.  Currently just one CPU is
responsible for the page pinning, which usually boils down to page
clearing time-wise, so the ways to optimize this are buying a faster
CPU ;-) or using more of the CPUs you already have.

Parallelize with ktask.  Refactor so workqueue workers pin with the mm
of the calling thread, and to enable an undo callback for ktask to
handle errors during page pinning.

Performance results appear later in the series.

Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Hongbo Yao <yaohongbo@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Tested-by: Hongbo Yao <yaohongbo@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>