[virtio-dev] Re: [PATCH v2 0/2] transport-pci: Introduce legacy registers access using AQ

Jason Wang
2023-05-16T03:38:03Z

在 2023/5/16 02:01, Michael S. Tsirkin 写道:
> On Mon, May 15, 2023 at 06:00:02PM +0000, Parav Pandit wrote:
>>> From: Michael S. Tsirkin <mst@redhat.com>
>>> Sent: Monday, May 15, 2023 1:56 PM
>>>
>>> On Mon, May 15, 2023 at 05:51:05PM +0000, Parav Pandit wrote:
>>>>> From: Michael S. Tsirkin <mst@redhat.com>
>>>>> Sent: Monday, May 15, 2023 1:45 PM
>>>>>
>>>>> On Mon, May 15, 2023 at 03:49:44PM +0000, Parav Pandit wrote:
>>>>>> All legacy interface via AQ.
>>>>>> All modern interface access via PCI or its own transport between
>>>>>> driver and
>>>>> device.
>>>>>
>>>>> I am wondering however about the hypervisor notifications.
>>>>> Generally these are the most problematic aspect here I feel. For
>>>>> example, how does it interact with VIRTIO_F_NOTIF_CONFIG_DATA? And
>>>>> generally, having both guest and host be allowed to access device's BAR
>>> seems problematic.
>>>>> Can we reserve a PF BAR region for these things or is that too expensive?
>>>> VIRTIO_F_NOTIF_CONFIG_DATA is not present for the legacy.
>>> it is not but it just might be required, or it won't be there.
>>>
>> How can it be required if it not part of it?
>> I likely didn't follow your question/comment, can you please explain.
> VIRTIO_F_NOTIF_CONFIG_DATA is there presumably for a reason.
>
>>>> For modern device, guest driver will access the device own BAR directly with
>>> its own config_data anyway.
>>>> Should we reserve a region in the PF BAR for SF/SIOV device?, should device
>>> report which BAR/area to use for the given SF/SIOV device?
>>>> May be yes, those are different discussions with tradeoff to consider during
>>> SIOV discussions. It is not related to VFs.
>>>
>>> For SIOV it's a given. But we can do this for SRIOV: reserve a PF region per VF.
>> Each VF has its own BAR area for driver notifications.
> But it is passed through to guest presumably.

Probably not in the case of VIRTIO_F_NOTIF_CONFIG_DATA. Did you see any
problem if we do mediation here except for some performance penalty?

Thanks