On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:

This series tries to access virtqueue metadata through kernel virtual
address instead of copy_user() friends since they had too much
overheads like checks, spec barriers or even hardware feature
toggling.

I think it's a reasonable approach.
However I need to look at whether and which mmu notifiers are invoked before
writeback. Do you know?

Test shows about 24% improvement on TX PPS. It should benefit other
cases as well.

Changes from V2:
- fix buggy range overlapping check
- tear down MMU notifier during vhost ioctl to make sure invalidation
  request can read metadata userspace address and vq size without
  holding vq mutex.
Changes from V1:
- instead of pinning pages, use MMU notifier to invalidate vmaps and
  remap duing metadata prefetch
- fix build warning on MIPS

Jason Wang (5):
  vhost: generalize adding used elem
  vhost: fine grain userspace memory accessors
  vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch()
  vhost: introduce helpers to get the size of metadata area
  vhost: access vq metadata through kernel virtual address

 drivers/vhost/net.c   |   4 +-
 drivers/vhost/vhost.c | 416 +++++++++++++++++++++++++++++++++++++-----
 drivers/vhost/vhost.h |  15 +-
 3 files changed, 384 insertions(+), 51 deletions(-)

-- 
2.17.1