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

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

On 8/17/2023 4:31 PM, Uminski, Piotr wrote:
>
>> -----Original Message-----
>> From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis-
>> open.org> On Behalf Of Zhu, Lingshan
>> Sent: Tuesday, August 15, 2023 1:30 PM
>> To: Jason Wang <jasowang@redhat.com>
>> Cc: mst@redhat.com; eperezma@redhat.com; cohuck@redhat.com; virtio-
>> comment@lists.oasis-open.org; virtio-dev@lists.oasis-open.org
>> Subject: [virtio-comment] Re: [RFC PATCH 4/5] virtqueue: constraints for
>> virtqueue state
>>
>>
>>
>> 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
> It should be possible to set Virtqueue State in two states:
>   - Before DRIVER_OK - as a part of the queue creation at target system
> -  After SUSPEND - when the device was activated and then suspended
> Setting state on active device can produce random results and should be forbidden.
> We may allow to get Virtqueue State on active device, without SUSPEND. However, we should not mandate the device
> to report correct value - on some implementations it may be impossible without suspend.
I agree
>>>> +
>>>> +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
>>>> +
>>>> +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
>>>>
>>
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