From: Jason Wang <jasowang@redhat.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Si-Wei Liu <si-wei.liu@oracle.com>,
elic@nvidia.com, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, virtio-dev@lists.oasis-open.org
Subject: Re: [virtio-dev] Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero
Date: Fri, 5 Mar 2021 11:01:28 +0800 [thread overview]
Message-ID: <71fd3f74-00ba-f085-27e9-6a0d21c9a93f@redhat.com> (raw)
In-Reply-To: <20210304145000.149706ae.cohuck@redhat.com>
On 2021/3/4 9:50 下午, Cornelia Huck wrote:
> On Thu, 4 Mar 2021 16:24:16 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> On 2021/3/3 4:29 下午, Cornelia Huck wrote:
>>> On Wed, 3 Mar 2021 12:01:01 +0800
>>> Jason Wang <jasowang@redhat.com> wrote:
>>>
>>>> On 2021/3/2 8:08 下午, Cornelia Huck wrote:
>>>>> On Mon, 1 Mar 2021 11:51:08 +0800
>>>>> Jason Wang <jasowang@redhat.com> wrote:
>>>>>
>>>>>> On 2021/3/1 5:25 上午, Michael S. Tsirkin wrote:
>>>>>>> On Fri, Feb 26, 2021 at 04:19:16PM +0800, Jason Wang wrote:
>>>>>>>> On 2021/2/26 2:53 上午, Michael S. Tsirkin wrote:
>>>>>>>>> Confused. What is wrong with the above? It never reads the
>>>>>>>>> field unless the feature has been offered by device.
>>>>>>>> So the spec said:
>>>>>>>>
>>>>>>>> "
>>>>>>>>
>>>>>>>> The following driver-read-only field, max_virtqueue_pairs only exists if
>>>>>>>> VIRTIO_NET_F_MQ is set.
>>>>>>>>
>>>>>>>> "
>>>>>>>>
>>>>>>>> If I read this correctly, there will be no max_virtqueue_pairs field if the
>>>>>>>> VIRTIO_NET_F_MQ is not offered by device? If yes the offsetof() violates
>>>>>>>> what spec said.
>>>>>>>>
>>>>>>>> Thanks
>>>>>>> I think that's a misunderstanding. This text was never intended to
>>>>>>> imply that field offsets change beased on feature bits.
>>>>>>> We had this pain with legacy and we never wanted to go back there.
>>>>>>>
>>>>>>> This merely implies that without VIRTIO_NET_F_MQ the field
>>>>>>> should not be accessed. Exists in the sense "is accessible to driver".
>>>>>>>
>>>>>>> Let's just clarify that in the spec, job done.
>>>>>> Ok, agree. That will make things more eaiser.
>>>>> Yes, that makes much more sense.
>>>>>
>>>>> What about adding the following to the "Basic Facilities of a Virtio
>>>>> Device/Device Configuration Space" section of the spec:
>>>>>
>>>>> "If an optional configuration field does not exist, the corresponding
>>>>> space is still present, but reserved."
>>>> This became interesting after re-reading some of the qemu codes.
>>>>
>>>> E.g in virtio-net.c we had:
>>>>
>>>> *static VirtIOFeature feature_sizes[] = {
>>>> {.flags = 1ULL << VIRTIO_NET_F_MAC,
>>>> .end = endof(struct virtio_net_config, mac)},
>>>> {.flags = 1ULL << VIRTIO_NET_F_STATUS,
>>>> .end = endof(struct virtio_net_config, status)},
>>>> {.flags = 1ULL << VIRTIO_NET_F_MQ,
>>>> .end = endof(struct virtio_net_config, max_virtqueue_pairs)},
>>>> {.flags = 1ULL << VIRTIO_NET_F_MTU,
>>>> .end = endof(struct virtio_net_config, mtu)},
>>>> {.flags = 1ULL << VIRTIO_NET_F_SPEED_DUPLEX,
>>>> .end = endof(struct virtio_net_config, duplex)},
>>>> {.flags = (1ULL << VIRTIO_NET_F_RSS) | (1ULL <<
>>>> VIRTIO_NET_F_HASH_REPORT),
>>>> .end = endof(struct virtio_net_config, supported_hash_types)},
>>>> {}
>>>> };*
>>>>
>>>> *It has a implict dependency chain. E.g MTU doesn't presnet if
>>>> DUPLEX/RSS is not offered ...
>>>> *
>>> But I think it covers everything up to the relevant field, no? So MTU
>>> is included if we have the feature bit, even if we don't have
>>> DUPLEX/RSS.
>>>
>>> Given that a config space may be shorter (but must not collapse
>>> non-existing fields), maybe a better wording would be:
>>>
>>> "If an optional configuration field does not exist, the corresponding
>>> space will still be present if it is not at the end of the
>>> configuration space (i.e., further configuration fields exist.)
>>
>> This should work but I think we need to define the end of configuration
>> space first?
> What about sidestepping this:
>
> "...the corresponding space will still be present, unless no further
> configuration fields exist."
>
> ?
It might work. (I wonder maybe we can give some example in the spec).
Thanks
>
>>> This
>>> implies that a given field, if it exists, is always at the same offset
>>> from the beginning of the configuration space."
next prev parent reply other threads:[~2021-03-05 3:01 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 11:54 [PATCH] vdpa/mlx5: set_features should allow reset to zero Si-Wei Liu
2021-02-21 14:44 ` Eli Cohen
2021-02-21 21:52 ` Michael S. Tsirkin
2021-02-22 6:05 ` Eli Cohen
2021-02-23 9:26 ` Michael S. Tsirkin
2021-02-23 9:48 ` Jason Wang
2021-02-23 9:55 ` Michael S. Tsirkin
2021-02-22 4:14 ` Jason Wang
2021-02-22 7:34 ` Michael S. Tsirkin
2021-02-23 1:12 ` Si-Wei Liu
2021-02-23 2:03 ` Jason Wang
2021-02-23 13:26 ` Michael S. Tsirkin
2021-02-23 19:35 ` Si-Wei Liu
2021-02-24 3:20 ` Jason Wang
2021-02-24 5:17 ` Michael S. Tsirkin
2021-02-24 6:02 ` Jason Wang
2021-02-24 6:45 ` Eli Cohen
2021-02-24 6:47 ` Michael S. Tsirkin
2021-02-24 6:55 ` Jason Wang
2021-02-24 7:12 ` Michael S. Tsirkin
2021-02-24 12:40 ` Eli Cohen
2021-02-24 7:17 ` Eli Cohen
2021-02-24 5:04 ` Michael S. Tsirkin
2021-02-24 6:04 ` Jason Wang
2021-02-24 6:46 ` Michael S. Tsirkin
2021-02-24 6:53 ` Jason Wang
2021-02-24 7:17 ` Michael S. Tsirkin
[not found] ` <babc654d-8dcd-d8a2-c3b6-d20cc4fc554c@redhat.com>
2021-02-24 8:43 ` Michael S. Tsirkin
2021-02-24 9:30 ` Jason Wang
2021-02-28 21:30 ` Michael S. Tsirkin
2021-03-01 3:53 ` Jason Wang
2021-02-24 18:24 ` Si-Wei Liu
2021-02-26 0:56 ` Si-Wei Liu
2021-02-28 21:27 ` Michael S. Tsirkin
2021-03-01 18:08 ` Si-Wei Liu
2021-02-28 21:28 ` Michael S. Tsirkin
2021-02-28 21:34 ` Michael S. Tsirkin
2021-03-01 3:56 ` Jason Wang
2021-03-02 9:47 ` Michael S. Tsirkin
2021-03-02 10:53 ` Jason Wang
2021-12-11 1:44 ` vdpa legacy guest support (was Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero) Si-Wei Liu
2021-12-12 9:26 ` Michael S. Tsirkin
2021-12-13 3:02 ` Jason Wang
2021-12-13 8:06 ` Michael S. Tsirkin
2021-12-13 8:57 ` Jason Wang
2021-12-13 10:42 ` Michael S. Tsirkin
2021-12-14 1:13 ` Si-Wei Liu
2021-12-14 1:59 ` Si-Wei Liu
2021-12-14 3:01 ` Jason Wang
2021-12-14 5:06 ` Michael S. Tsirkin
2021-12-15 1:05 ` Si-Wei Liu
2021-12-15 2:06 ` Jason Wang
2021-12-15 20:52 ` Si-Wei Liu
2021-12-15 21:33 ` Michael S. Tsirkin
2021-12-16 2:01 ` Si-Wei Liu
2021-12-16 2:53 ` Jason Wang
2021-12-16 22:32 ` Si-Wei Liu
2021-12-17 1:57 ` Jason Wang
2021-12-17 2:00 ` Michael S. Tsirkin
2021-12-17 2:15 ` Jason Wang
2021-12-16 6:35 ` Michael S. Tsirkin
2021-12-16 3:43 ` Jason Wang
2021-12-17 1:08 ` Si-Wei Liu
2021-12-17 2:01 ` Jason Wang
2021-02-22 17:09 ` [PATCH] vdpa/mlx5: set_features should allow reset to zero Si-Wei Liu
2021-02-23 2:03 ` Jason Wang
2021-02-23 9:25 ` Michael S. Tsirkin
2021-02-23 9:46 ` Jason Wang
2021-02-23 10:01 ` Michael S. Tsirkin
2021-02-23 10:17 ` Jason Wang
2021-02-24 9:40 ` Jason Wang
2021-02-23 10:04 ` [virtio-dev] " Cornelia Huck
2021-02-23 10:31 ` Jason Wang
2021-02-23 10:58 ` Cornelia Huck
2021-02-24 9:29 ` Jason Wang
2021-02-24 11:12 ` Cornelia Huck
2021-02-25 4:36 ` Jason Wang
2021-02-25 13:26 ` Cornelia Huck
2021-02-25 18:53 ` Michael S. Tsirkin
2021-02-26 8:19 ` Jason Wang
2021-02-28 21:25 ` Michael S. Tsirkin
2021-03-01 3:51 ` Jason Wang
2021-03-02 12:08 ` Cornelia Huck
[not found] ` <5f6972fe-7246-b622-958d-9cab8dd98e21@redhat.com>
2021-03-03 8:29 ` Cornelia Huck
2021-03-04 8:24 ` Jason Wang
2021-03-04 13:50 ` Cornelia Huck
2021-03-05 3:01 ` Jason Wang [this message]
2021-02-23 12:26 ` Michael S. Tsirkin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=71fd3f74-00ba-f085-27e9-6a0d21c9a93f@redhat.com \
--to=jasowang@redhat.com \
--cc=cohuck@redhat.com \
--cc=elic@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mst@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=si-wei.liu@oracle.com \
--cc=virtio-dev@lists.oasis-open.org \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).