[virtio-dev] Re: [virtio-comment] Re: [PATCH 09/11] transport-pci: Describe PCI MMR dev config registers

Michael S. Tsirkin
2023-04-10T06:40:00Z

On Mon, Apr 10, 2023 at 02:20:16PM +0800, Jason Wang wrote:
> On Mon, Apr 10, 2023 at 2:15 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Apr 10, 2023 at 09:33:32AM +0800, Jason Wang wrote:
> > > This is fine for vDPA but not for virtio if the design can only work
> > > for some specific setups (OSes/archs).
> > >
> > > Thanks
> >
> > Well virtio legacy has a long history of documenting existing hacks :)
>
> Exactly, so the legacy behaviour is not (or can't be) defined by the
> spec but the codes.

I mean driver behaviour derives from the code but we do document it in
the spec to help people build devices.

> > But yes, VIRTIO_F_ORDER_PLATFORM has to be documented.
> > And we have to decide what to do about ACCESS_PLATFORM since
> > there's a security problem if device allows not acking it.
> > Two options:
> > - relax the rules a bit and say device will assume ACCESS_PLATFORM
> > is acked anyway
>
> This will break legacy drivers which assume physical addresses.

not that they are not already broken.

> > - a new flag that is insecure (so useful for sec but useless for dpdk) but optional
>
> This looks like a new "hack" for the legacy hacks.

it's not just for legacy.

> And what about ORDER_PLATFORM, I don't think we can modify legacy drivers...
>
> Thanks

You play some tricks with shadow VQ I guess.

--
MST