linux-kernel - Re: [PATCH v2] vdpa/vp_vdpa: Check queue number of vdpa device from add

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Message-ID: <CACGkMEuEXAioOvDAZkkkcKc+vkz5Py29jYrC+uTUVG-bahx8Lw@mail.gmail.com>
Date:   Fri, 9 Jun 2023 10:30:27 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Angus Chen <angus.chen@...uarmicro.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vdpa/vp_vdpa: Check queue number of vdpa device from add_config

On Fri, Jun 9, 2023 at 3:45 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Jun 08, 2023 at 05:01:24PM +0800, Angus Chen wrote:
> > When add virtio_pci vdpa device,check the vqs number of device cap
> > and max_vq_pairs from add_config.
> > Simply starting from failing if the provisioned #qp is not
> > equal to the one that hardware has.

I think I kind of agree with Michael, I don't see any obvious
advantages to allow usersapce to configure max_vqp if it can't be
provisioned dynamically. What's wrong if we just stick the current
approach that doesn't accept max_vqp?

A better approach is to tweak the vdpa tool to display the legal
attributes that can be provisioned.

> >
> > Signed-off-by: Angus Chen <angus.chen@...uarmicro.com>
>
> I am not sure about this one. How does userspace know
> which values are legal?

vdpa mgmtdev show can gives hints like:

max_supported_vqs 3

>
> If there's no way then maybe we should just cap the value
> to what device can support but otherwise keep the device
> working.

This seems conflict to how other drivers (like mlx5) did:

        if (add_config->mask & BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MAX_VQP)) {
                if (add_config->net.max_vq_pairs > max_vqs / 2)
                        return -EINVAL;
                max_vqs = min_t(u32, max_vqs, 2 * add_config->net.max_vq_pairs);
        } else {
                max_vqs = 2;
        }

Thanks

>
> > ---
> > v1: Use max_vqs from add_config
> > v2: Just return fail if max_vqs from add_config is not same as device
> >       cap. Suggested by jason.
> >
> >  drivers/vdpa/virtio_pci/vp_vdpa.c | 35 ++++++++++++++++++-------------
> >  1 file changed, 21 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > index 281287fae89f..c1fb6963da12 100644
> > --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> > +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > @@ -480,32 +480,39 @@ static int vp_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
> >       u64 device_features;
> >       int ret, i;
> >
> > -     vp_vdpa = vdpa_alloc_device(struct vp_vdpa, vdpa,
> > -                                 dev, &vp_vdpa_ops, 1, 1, name, false);
> > -
> > -     if (IS_ERR(vp_vdpa)) {
> > -             dev_err(dev, "vp_vdpa: Failed to allocate vDPA structure\n");
> > -             return PTR_ERR(vp_vdpa);
> > +     if (add_config->mask & BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MAX_VQP)) {
> > +             if (add_config->net.max_vq_pairs != (v_mdev->max_supported_vqs / 2)) {
> > +                     dev_err(&pdev->dev, "max vqs 0x%x should be equal to 0x%x which device has\n",
> > +                             add_config->net.max_vq_pairs*2, v_mdev->max_supported_vqs);
> > +                     return -EINVAL;
> > +             }
> >       }
> >
> > -     vp_vdpa_mgtdev->vp_vdpa = vp_vdpa;
> > -
> > -     vp_vdpa->vdpa.dma_dev = &pdev->dev;
> > -     vp_vdpa->queues = vp_modern_get_num_queues(mdev);
> > -     vp_vdpa->mdev = mdev;
> > -
> >       device_features = vp_modern_get_features(mdev);
> >       if (add_config->mask & BIT_ULL(VDPA_ATTR_DEV_FEATURES)) {
> >               if (add_config->device_features & ~device_features) {
> > -                     ret = -EINVAL;
> >                       dev_err(&pdev->dev, "Try to provision features "
> >                               "that are not supported by the device: "
> >                               "device_features 0x%llx provisioned 0x%llx\n",
> >                               device_features, add_config->device_features);
> > -                     goto err;
> > +                     return -EINVAL;
> >               }
> >               device_features = add_config->device_features;
> >       }
> > +
> > +     vp_vdpa = vdpa_alloc_device(struct vp_vdpa, vdpa,
> > +                                 dev, &vp_vdpa_ops, 1, 1, name, false);
> > +
> > +     if (IS_ERR(vp_vdpa)) {
> > +             dev_err(dev, "vp_vdpa: Failed to allocate vDPA structure\n");
> > +             return PTR_ERR(vp_vdpa);
> > +     }
> > +
> > +     vp_vdpa_mgtdev->vp_vdpa = vp_vdpa;
> > +
> > +     vp_vdpa->vdpa.dma_dev = &pdev->dev;
> > +     vp_vdpa->queues = v_mdev->max_supported_vqs;
> > +     vp_vdpa->mdev = mdev;
> >       vp_vdpa->device_features = device_features;
> >
> >       ret = devm_add_action_or_reset(dev, vp_vdpa_free_irq_vectors, pdev);
> > --
> > 2.25.1
>