From: "Alex Bennée" <alex.bennee@linaro.org>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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 13:21:04 +0000 [thread overview]
Message-ID: <871rd86xrf.fsf@linaro.org> (raw)
In-Reply-To: <YDOsP1pWUS+hXiBX@work-vm>
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.
>
>> - 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
next prev parent reply other threads:[~2021-02-22 13:27 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 [this message]
2021-02-22 13:27 ` Dr. David Alan Gilbert
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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