Re: [PATCH 0/2] Search the split vq desc and avail in RO areas

[David Marchand <david.marchand@redhat.com>]

On Thu, Jun 5, 2025 at 4:55 PM Eugenio Perez Martin <eperezma@redhat.com> wrote:
>
> On Thu, Jun 5, 2025 at 1:50 PM David Marchand <david.marchand@redhat.com> wrote:
> >
> > On Thu, Jun 5, 2025 at 1:36 PM Eugenio Pérez <eperezma@redhat.com> wrote:
> > >
> > > QEMU's shadow virtqueue and VDUSE exposes these areas as read-only. If
> > > we don't change it, vhost_iova_to_vva do not consider them as valid and
> > > returns that they're not found.
> > >
> > > Eugenio Pérez (2):
> > >   vhost: search the split vq desc and avail in RO areas
> > >   vhost: search the packed vq driver area in RO areas
> > >
> > >  lib/vhost/vhost.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > At a quick glance, no need for two patches.
> >
>
> Sure I can respin with both squashed.
>
> > Sorry, the implication of this issue is not clear to me.
> > What is the impact from a user pov?
> >
>
> QEMU maps the CVQ descriptors and avail vring through as read only
> maps in the case of vDPA. But DPDK is looking for them with RW
> permissions, so the vhost_iova_to_vva function never selects the right
> one as valid.
>
> Looking for them with RO still picks the map if it is mapped as RW,
> but the reverse is not true.

Ok, thanks.
Well, it's better, but still hard to tell how this impacts existing
usecases :-).
After discussing with Maxime, I understand that the shadow CVQ just
can't work => blocking multi queue support with vduse for example.
This is the type of high level impact I was looking for.

> Let me know if you want me to respin the series with this comment too!

Ideally yes, but maybe Maxime can do it when applying.


-- 
David Marchand