[virtio-dev] Re: [virtio-comment] Re: [RFC PATCH 4/5] virtqueue: constraints for virtqueue state

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 8/21/2023 5:26 PM, Eugenio Perez Martin wrote:
> On Fri, Aug 18, 2023 at 11:44 AM Zhu, Lingshan <lingshan.zhu@intel.com> wrote:
>>
>>
>> On 8/17/2023 11:19 PM, Eugenio Perez Martin wrote:
>>> On Tue, Aug 15, 2023 at 1:30 PM Zhu, Lingshan <lingshan.zhu@intel.com> wrote:
>>>>
>>>> On 8/15/2023 8:34 AM, Jason Wang wrote:
>>>>> On Mon, Aug 14, 2023 at 7:29 PM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>>>>>> This commit specifies the constraints of the virtqueue state,
>>>>>> and the actions should be taken by the device when SUSPEND
>>>>>> and DRIVER_OK is set
>>>>>>
>>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
>>>>>> ---
>>>>>>     content.tex | 31 +++++++++++++++++++++++++++++++
>>>>>>     1 file changed, 31 insertions(+)
>>>>>>
>>>>>> diff --git a/content.tex b/content.tex
>>>>>> index 43bd5de..f6ac581 100644
>>>>>> --- a/content.tex
>>>>>> +++ b/content.tex
>>>>>> @@ -587,6 +587,37 @@ \subsection{\field{Used State} Field}
>>>>>>
>>>>>>     See also \ref{sec:Packed Virtqueues / Driver and Device Ring Wrap Counters}.
>>>>>>
>>>>>> +\drivernormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated, the driver MUST set SUSPEND in \field{device status}
>>>>>> +first before getting or setting Virtqueue State of any virtqueues.
>>>>> I don't get why this is a must. It could be useful for debugging.
>>>> To avoid race conditions with the device and make the device
>>>> implementation easier
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiaged but VIRTIO_RING_F_PACKED not been negotiated,
>>>>> typo
>>>> yes
>>>>>> +the driver MUST NOT access \field{Used State} of any virtqueues, it should use the
>>>>>> +used index in the used ring.
>>>>>> +
>>>>>> +\devicenormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio Device / Virtqueue State}
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated but SUSPEND is not set in \field{device status},
>>>>>> +the device MUST ignore any accesses against Virtqueue State of any virtqueues.
>>>>> Btw, do we need to clarify the behavior of ring reset after suspending?
>>>> I think once suspended, the device should ignore resetting a queue
>>> Actually shadow virtqueue could benefit from the ability to change vq
>>> properties (addresses) while the device is suspended, and then just
>>> resume it. I've been told that ring reset is overkill for that.
>> If ring reset is overkill, is SUSPEND even more overkill?
> It depends on the cost of recreating the vq in the device I think. But
> it has more to do with *what* is changed in the vq, as it seems some
> parameters (vq size) has more impact than others like vq address. The
> way to stop the device does not affect, but ring reset offers the
> possibility of change all of the parameters already.
>
> Adding Si-Wei and Dragos here, as they pointed it out in the
> virtio-networking upstream meeting.
>
>>> But probably it is better to address it on top, with another feature flag.
>> I think if we want to changing the vq properties, there must be a
>> mechanism to
>> stop the queue then resume the queue.
>>
>> How about allow setting queue_enable = 0 to stop it and =1 to resume and
>> force it reinitialize?
>>
> Yes, I think that is better suited. But maybe this is better to be
> added on top, so we maintain this series small.
OK, I can work out a patch in this series implementing it.
And as discussed in another thread with Jason in this series, it
is better to forbid resetting a vq after SUSPEND.

Thanks
>
> Thanks!
>
>> Thanks
>> Zhu Lingshan
>>>>>> +
>>>>>> +When VIRTIO_F_QUEUE_STATE has been negotiated but VIRTIO_RING_F_PACKED is not,
>>>>>> +the device MUST ignore any accesses against \field{Used State}.
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiaged, the device MUST reset
>>>>>> +the Virtqueue State of every virtqueue upon a reset.
>>>>> Need to define the meaning of "reset" this is important for packed virtqueue.
>>>> I will remove this as Stefan suggested.
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE and VIRTIO_RING_F_PACKED have been negotiaged, when SUSPEND is set,
>>>>>> +the device MUST record the Virtqueue State of every enabled virtqueue
>>>>>> +in \field{Available State} and \field{Used State} respectively,
>>>>>> +and correspondingly restore the Virtqueue State of every enabled virtqueue
>>>>>> +from \field{Avaiable State} and \field{Used State} when DRIVER_OK is set.
>>>>> We can just let the device report those states in any case then we
>>>>> don't need to care about those details, or did you see any blockers?
>>>> Agree, I will add the definition of used_state of splitted vq in the
>>>> next version
>>>>
>>>> Thanks
>>>>> Thanks
>>>>>
>>>>>> +
>>>>>> +If VIRTIO_F_QUEUE_STATE has been negotiated but VIRTIO_RING_F_PACKED has been not, when SUSPEND is set,
>>>>>> +the device MUST record the available state of every enabled virtqueue in \field{Available State},
>>>>>> +and restore the available state of every enabled virtqueue from \field{Avaiable State}
>>>>>> +when DRIVER_OK is set.
>>>>>> +
>>>>>>     \input{admin.tex}
>>>>>>
>>>>>>     \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
>>>>>> --
>>>>>> 2.35.3
>>>>>>
>
> This publicly archived list offers a means to provide input to the
>
> OASIS Virtual I/O Device (VIRTIO) TC.
>
>
>
> In order to verify user consent to the Feedback License terms and
>
> to minimize spam in the list archive, subscription is required
>
> before posting.
>
>
>
> Subscribe: virtio-comment-subscribe@lists.oasis-open.org
>
> Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org
>
> List help: virtio-comment-help@lists.oasis-open.org
>
> List archive: https://lists.oasis-open.org/archives/virtio-comment/
>
> Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf
>
> List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists
>
> Committee: https://www.oasis-open.org/committees/virtio/
>
> Join OASIS: https://www.oasis-open.org/join/
>


---------------------------------------------------------------------
To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org