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

Jason Wang
2023-05-11T07:21:09Z

On Thu, May 11, 2023 at 12:08 AM Parav Pandit <parav@nvidia.com> wrote:
>
>
>
> On 5/10/2023 12:22 AM, Jason Wang wrote:
> > On Wed, May 10, 2023 at 11:51 AM Jason Wang <jasowang@redhat.com> wrote:
>
> >
> > Just to make sure we are at the same page.
> >
> > 1) if the hardware has configq and we need to make it work for current
> > virtio-pci driver, hypervisor needs to trap guest PCI access and
> > translate it to configq command. This means the hypervisor needs to
> > hide the configq from guests. In this case the configq needs a
> > dedicated DMA address which is what PASID can help.
>
> > 2) if the hardware can report the device states, unless we want to
> > migrate L2 guest, hypervisor should hide it from L1, so PASID is
> > required to isolate the DMA for guest traffic and device state.
>
> A configq negotiates + discovers new fields for the PCI PF, VF, SF/SIOV
> devices over PCIe or other transports.
> So no need to hide/mediate for hw based devices, like cvq and like data vqs.

As discussed, I may misunderstand the function of the configq. If it
works like cvq, then yes. We don't need PASID.

But if we want to report device state via let's say migration q, it
requires PASID since it is used by the hypervisor.

Thanks

>
> For vdpa kind of use case it can work like cvq mediation, which I
> believe is happening without PASID today.
>
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