linux-kernel - Re: [PATCH 1/2] vdpa_sim: not reset state in vdpasim_queue

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Message-ID: <CAJaqyWejkbiwKK4O0qOObdf294YrzMeSRTVoWNzv75yQCvkJqQ@mail.gmail.com>
Date:   Thu, 19 Jan 2023 10:14:57 +0100
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, leiyang@...hat.com,
        Laurent Vivier <lvivier@...hat.com>, sgarzare@...hat.com,
        Zhu Lingshan <lingshan.zhu@...el.com>,
        virtualization@...ts.linux-foundation.org, si-wei.liu@...cle.com,
        linux-kernel@...r.kernel.org, lulu@...hat.com,
        Gautam Dawar <gdawar@...inx.com>, alvaro.karsz@...id-run.com
Subject: Re: [PATCH 1/2] vdpa_sim: not reset state in vdpasim_queue_ready

On Thu, Jan 19, 2023 at 4:16 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Thu, Jan 19, 2023 at 12:44 AM Eugenio Pérez <eperezma@...hat.com> wrote:
> >
> > vdpasim_queue_ready calls vringh_init_iotlb, which resets split indexes.
> > But it can be called after setting a ring base with
> > vdpasim_set_vq_state.
> >
> > Fix it by stashing them. They're still resetted in vdpasim_vq_reset.
> >
> > This was discovered and tested live migrating the vdpa_sim_net device.
> >
> > Fixes: 2c53d0f64c06 ("vdpasim: vDPA device simulator")
> > Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> > ---
> >  drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > index cb88891b44a8..8839232a3fcb 100644
> > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > @@ -66,6 +66,7 @@ static void vdpasim_vq_notify(struct vringh *vring)
> >  static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
> >  {
> >         struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> > +       uint16_t last_avail_idx = vq->vring.last_avail_idx;
> >
> >         vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false,
> >                           (struct vring_desc *)(uintptr_t)vq->desc_addr,
> > @@ -74,6 +75,7 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
> >                           (struct vring_used *)
> >                           (uintptr_t)vq->device_addr);
> >
> > +       vq->vring.last_avail_idx = last_avail_idx;
>
> Does this need to be serialized with the datapath?
>
> E.g in set_vq_state() we do:
>
> spin_lock(&vdpasim->lock);
> vrh->last_avail_idx = state->split.avail_index;
> spin_unlock(&vdpasim->lock);
>

vdpasim_queue_ready is called from vdpasim_set_vq_ready, which holds
these locks.

Maybe it's too much indirection and to embed vdpasim_queue_ready in
vdpasim_set_vq_ready would be clearer for the future?

Thanks!