Re: [Qemu-devel] [PATCH v2 0/6] vhost-user: Specify and implement device IOTLB support

[Michael S. Tsirkin]

On Fri, May 26, 2017 at 04:28:52PM +0200, Maxime Coquelin wrote:
> This series aims at specifying ans implementing the protocol update
> required to support device IOTLB with user backends.
> 
> In this second non-RFC version, main changes are:
>  - spec fixes and clarification
>  - rings information update has been restored back to ring enablement time
>  - Work around GCC 4.4.7 limitation wrt assignment in unnamed union at
> declaration time.
> 
> The series can be tested with vhost_iotlb_proto_v2 branch on my gitlab
> account[0].
> 
> The slave requests channel part is re-used from Marc-André's series submitted
> last year[1], with main changes from original version being request/feature
> names renaming and addition of the REPLY_ACK feature support.
> 
> Regarding IOTLB protocol, one noticeable change is the IOTLB miss request
> reply made optionnal (i.e. only if slave requests it by setting the
> VHOST_USER_NEED_REPLY flag in the message header). This change provides
> more flexibility in the backend implementation of the feature.
> 
> The protocol is very close to kernel backends, except that a new
> communication channel is introduced to enable the slave to send
> requests to the master.
> 
> [0]: 
> https://gitlab.com/mcoquelin/dpdk-next-virtio/commits/vhost_iotlb_proto_v2
> [1]: https://lists.gnu.org/archive/html/qemu-devel/2016-04/msg00095.html

Overall, this looks good to me. I do think patch 3 isn't a good idea
though, if slave wants something let it request it.

Need to find out why does vhost in kernel want the used ring iotlb at
start time - especially considering we aren't even guaranteed one entry
covers the whole ring, and invalidates should affect all addresses at
least in theory.


> Marc-André Lureau (2):
>   vhost-user: add vhost_user to hold the chr
>   vhost-user: add slave-req-fd support
> 
> Maxime Coquelin (4):
>   vhost: propagate errors in vhost_device_iotlb_miss()
>   vhost: rework IOTLB messaging
>   vhost: extend ring information update for IOTLB to all rings
>   spec/vhost-user spec: Add IOMMU support
> 
>  docs/specs/vhost-user.txt         | 118 ++++++++++++++++++++++++-
>  hw/virtio/vhost-backend.c         | 130 ++++++++++++++++------------
>  hw/virtio/vhost-user.c            | 177 
> +++++++++++++++++++++++++++++++++++++-
>  hw/virtio/vhost.c                 |  27 ++++--
>  include/hw/virtio/vhost-backend.h |  23 +++--
>  include/hw/virtio/vhost.h         |   2 +-
>  6 files changed, 397 insertions(+), 80 deletions(-)
> 
> -- 
> 2.9.4