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

Michael S. Tsirkin
2023-05-11T11:35:34Z

On Thu, May 11, 2023 at 03:20:52PM +0800, Jason Wang wrote:
> 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

I don't exactly get this part. With SRIOV migration q normally would be
part of the PF, accessing hypervisor memory.

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