From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: "Sergio Lopez" <slp@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
qemu-devel@nongnu.org, "Stefan Hajnoczi" <stefanha@redhat.com>,
"rust-vmm@lists.opendev.org" <rust-vmm@lists.opendev.org>,
"Marc-André Lureau" <marcandre.lureau@redhat.com>
Subject: Re: vhost reply_ack negotiation (a.k.a differences in vhost-user behaviour with libvhost-user and vhost-user-backend.rs)
Date: Mon, 22 Feb 2021 13:27:22 +0000 [thread overview]
Message-ID: <YDOxOv4w3J68b+uo@work-vm> (raw)
In-Reply-To: <871rd86xrf.fsf@linaro.org>
* Alex Bennée (alex.bennee@linaro.org) wrote:
>
> Dr. David Alan Gilbert <dgilbert@redhat.com> writes:
>
> > * Alex Bennée (alex.bennee@linaro.org) wrote:
> >> Hi,
> >>
> >> I finally got a chance to get down into the guts of vhost-user while
> >> attempting to port my original C RPMB daemon to Rust using the
> >> vhost-user-backend and related crates. I ended up with this hang during
> >> negotiation:
> >>
> >> startup
> >>
> >> vhost_user_write req:1 flags:0x1
> >> vhost_user_read_start
> >> vhost_user_read req:1 flags:0x5
> >> vhost_user_backend_init: we got 170000000
>
> GET_FEATURES
>
> >> vhost_user_write req:15 flags:0x1
> >> vhost_user_read_start
> >> vhost_user_read req:15 flags:0x5
> >> vhost_user_set_protocol_features: 2008
> >> vhost_user_write req:16 flags:0x1
> >> vhost_user_write req:3 flags:0x1
> >> vhost_user_write req:1 flags:0x1
> >> vhost_user_read_start
> >> vhost_user_read req:1 flags:0x5
> >> vhost_user_write req:13 flags:0x1
> >>
> >> kernel initialises device
> >>
> >> virtio_rpmb virtio1: init done!
> >> vhost_user_write req:13 flags:0x1
> >> vhost_dev_set_features: 130000000
> >> vhost_user_set_features: 130000000
>
> SET_FEATURES
>
> >> vhost_user_write req:2 flags:0x1
> >> vhost_user_write req:5 flags:0x9
> >> vhost_user_read_start
> >>
> <snip>
> >>
> >> - Should QEMU have preserved VhostUserVirtioFeatures::PROTOCOL_FEATURES
> >> when doing the eventual VHOST_USER_SET_FEATURES reply?
> >>
> >> - Is vhost.rs being to strict or libvhost-user too lax in interpreting
> >> the negotiated features before processing the ``need_reply`` [Bit 3]
> >> field of the messages?
> >
> > I think vhost.rs is being correctly strict - but there would be no harm
> > in it flagging that you'd hit an inconsistency if it finds a need_reply
> > without the feature.
>
> But the feature should have been negotiated. So unless the slave can
> assume it is enabled because it asked I think QEMU is in the wrong by
> not preserving the feature bits in it's SET_FEATURES reply. We just gets
> away with it with libvhostuser being willing to reply anyway.
Oh I wasn't trying to reply to that bit; I can never remember how the
vhost/virtio feature bit negotiation works...
Dave
> >
> >> - are VHOST_USER_SET_MEM_TABLE to VHOST_USER_SET_INFLIGHT_FD included
> >> in the "list of the ones that do" require replies or do they only
> >> reply when REPLY_ACK has been negotiated as the ambiguous "seealso::"
> >> box out seems to imply?
> >
> > set_mem_table gives a reply when postcopy is enabled (and then qemu
> > replies to the reply!) but otherwise doesn't.
> > (Note there's an issue opened for .rs to support ADD_MEM_REGION
> > since it's a lot better than SET_MEM_TABLE which has a fixed size table
> > that's small).
>
> Thanks for the heads up.
>
> >
> > Dave
> >
> >> Currently I have some hacks in:
> >>
> >> https://github.com/stsquad/vhost/tree/my-hacks
> >>
> >> which gets my daemon booting up to the point we actually need to do a
> >> transaction. However I won't submit a PR until I've worked out exactly
> >> where the problems are.
> >>
> >> --
> >> Alex Bennée
> >>
>
>
> --
> Alex Bennée
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
next prev parent reply other threads:[~2021-02-22 13:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 16:04 vhost reply_ack negotiation (a.k.a differences in vhost-user behaviour with libvhost-user and vhost-user-backend.rs) Alex Bennée
2021-02-22 13:06 ` Dr. David Alan Gilbert
2021-02-22 13:21 ` Alex Bennée
2021-02-22 13:27 ` Dr. David Alan Gilbert [this message]
2021-02-23 10:23 ` [Rust-VMM] " Jiang Liu
2021-02-26 19:58 ` Raphael Norwitz
2021-02-26 21:25 ` Raphael Norwitz
2021-02-27 12:23 ` Alex Bennée
2021-02-23 11:44 ` Michael S. Tsirkin
2021-02-25 4:19 ` [Rust-VMM] " Dylan Reid
2021-02-25 6:36 ` Keiichi Watanabe
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