linux-kernel - Re: [PATCH] vdpa: conditionally fill max max queue pair for stats

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Date:   Tue, 13 Dec 2022 10:17:25 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Eli Cohen <elic@...dia.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vdpa: conditionally fill max max queue pair for stats

On Tue, Dec 13, 2022 at 03:12:23PM +0800, Jason Wang wrote:
> On Wed, Sep 7, 2022 at 4:11 PM Eli Cohen <elic@...dia.com> wrote:
> >
> > > From: Jason Wang <jasowang@...hat.com>
> > > Sent: Wednesday, 7 September 2022 9:53
> > > To: Eli Cohen <elic@...dia.com>
> > > Cc: mst@...hat.com; virtualization@...ts.linux-foundation.org; linux-
> > > kernel@...r.kernel.org
> > > Subject: Re: [PATCH] vdpa: conditionally fill max max queue pair for stats
> > >
> > > On Wed, Sep 7, 2022 at 2:11 PM Eli Cohen <elic@...dia.com> wrote:
> > > >
> > > > > From: Jason Wang <jasowang@...hat.com>
> > > > > Sent: Wednesday, 7 September 2022 9:01
> > > > > To: mst@...hat.com; jasowang@...hat.com; Eli Cohen
> > > <elic@...dia.com>;
> > > > > virtualization@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
> > > > > Subject: [PATCH] vdpa: conditionally fill max max queue pair for stats
> > > > >
> > > > > For the device without multiqueue feature, we will read 0 as
> > > > > max_virtqueue_pairs from the config.
> > > > If this is the case for other vdpa vendor drivers, shouldn't we fix it there?
> > > After all,
> > > > config->max_virtqueue_pairs should always show valid values.
> > >
> > > Not for the case when the device doesn't offer MQ. According to the
> > > spec, the max_virtqueue_pairs doesn't exist in this case.
> > >
> > I see, thanks.
> >
> > > >
> > > > > So if we fill
> > > > > VDPA_ATTR_DEV_NET_CFG_MAX_VQP with the value we read from the
> > > > > config
> > > > > we will confuse the user.
> > > > >
> > > > > Fixing this by only filling the value when multiqueue is offered by
> > > > > the device so userspace can assume 1 when the attr is not provided.
> > > > >
> > > > > Fixes: 13b00b135665c("vdpa: Add support for querying vendor
> > > statistics")
> > > > > Cc: Eli Cohen <elic@...dia.com>
> > > > > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > > > > ---
> > > > >  drivers/vdpa/vdpa.c | 9 ++++-----
> > > > >  1 file changed, 4 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> > > > > index c06c02704461..bc328197263f 100644
> > > > > --- a/drivers/vdpa/vdpa.c
> > > > > +++ b/drivers/vdpa/vdpa.c
> > > > > @@ -894,7 +894,6 @@ static int vdpa_fill_stats_rec(struct vdpa_device
> > > > > *vdev, struct sk_buff *msg,
> > > > >  {
> > > > >       struct virtio_net_config config = {};
> > > > >       u64 features;
> > > > > -     u16 max_vqp;
> > > > >       u8 status;
> > > > >       int err;
> > > > >
> > > > > @@ -905,15 +904,15 @@ static int vdpa_fill_stats_rec(struct
> > > vdpa_device
> > > > > *vdev, struct sk_buff *msg,
> > > > >       }
> > > > >       vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
> > > > >
> > > > > -     max_vqp = __virtio16_to_cpu(true, config.max_virtqueue_pairs);
> > > > > -     if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP,
> > > > > max_vqp))
> > > > > -             return -EMSGSIZE;
> > > > > -
> > > > >       features = vdev->config->get_driver_features(vdev);
> > > > >       if (nla_put_u64_64bit(msg,
> > > > > VDPA_ATTR_DEV_NEGOTIATED_FEATURES,
> > > > >                             features, VDPA_ATTR_PAD))
> > > > >               return -EMSGSIZE;
> > > > >
> > > > > +     err = vdpa_dev_net_mq_config_fill(vdev, msg, features, &config);
> > > > > +     if (err)
> > > > > +             return err;
> > > > > +
> > > >
> > > > So that means that you can't read statistics when MQ is not supported. Is
> > > this worth sacrificing?
> > >
> > > vdpa_dev_net_mq_config_fill() will return 0 in the case of !MQ, so it
> > > should still work.
> >
> > Right, missed that.
> >
> > Reviewed-by: Eli Cohen <elic@...dia.com>
> 
> Michael, I don't see this is merged.
> 
> Any comments for this patch?
> 
> Thanks
> 

Will be in the pull. Working on it now, it's pretty big.

> >
> > >
> > > Thanks
> > >
> > >
> > > >
> > > > >       if (nla_put_u32(msg, VDPA_ATTR_DEV_QUEUE_INDEX, index))
> > > > >               return -EMSGSIZE;
> > > > >
> > > > > --
> > > > > 2.25.1
> > > >
> >