linux-kernel - Re: [PATCH v2] vp_vdpa: harden the logic of set status

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Date:   Tue, 6 Dec 2022 14:49:29 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Longpeng(Mike)" <longpeng2@...wei.com>
Cc:     stefanha@...hat.com, mst@...hat.com, sgarzare@...hat.com,
        eperezma@...hat.com, cohuck@...hat.com, arei.gonglei@...wei.com,
        yechuan@...wei.com, huangzhichao@...wei.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vp_vdpa: harden the logic of set status

On Tue, Dec 6, 2022 at 10:13 AM Longpeng(Mike) <longpeng2@...wei.com> wrote:
>
> From: Longpeng <longpeng2@...wei.com>
>
> 1. We should not set status to 0 when invoking vp_vdpa_set_status(),
>    trigger a warning in that case.
>
> 2. The driver MUST wait for a read of device_status to return 0 before
>    reinitializing the device. But we also don't want to keep us in an
>    infinite loop forever, so wait for 5s if we try to reset the device.
>
> Signed-off-by: Longpeng <longpeng2@...wei.com>
> ---
> Changes v1->v2:
>   - use WARN_ON instead of BUG_ON. [Stefano]
>   - use "warning + failed" instead of "infinite loop". [Jason, Stefano]
>   - use usleep_range instead of msleep (checkpatch). [Longpeng]
>
> ---
>  drivers/vdpa/virtio_pci/vp_vdpa.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
> index 13701c2a1963..a2d3b13ac646 100644
> --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> @@ -214,6 +214,9 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
>         struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
>         u8 s = vp_vdpa_get_status(vdpa);
>
> +       /* We should never be setting status to 0. */
> +       WARN_ON(status == 0);
> +
>         if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
>             !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
>                 vp_vdpa_request_irq(vp_vdpa);
> @@ -222,14 +225,33 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
>         vp_modern_set_status(mdev, status);
>  }
>
> +#define VP_VDPA_RESET_TMOUT_MS 5000 /* 5s */
> +
>  static int vp_vdpa_reset(struct vdpa_device *vdpa, bool clear)
>  {
>         struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
>         struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
>         u8 s = vp_vdpa_get_status(vdpa);
> +       unsigned long timeout;
>
>         vp_modern_set_status(mdev, 0);
>
> +       /*
> +        * As the virtio v1.1 spec (4.1.4.3.2) says: After writing 0 to
> +        * device_status, the driver MUST wait for a read of device_status
> +        * to return 0 before reinitializing the device.
> +        * To avoid keep us here forever, we only wait for 5 seconds.

s/keep/keeping/

> +        */
> +       timeout = jiffies + msecs_to_jiffies(VP_VDPA_RESET_TMOUT_MS);
> +       while (vp_modern_get_status(mdev)) {
> +               usleep_range(1000, 1500);
> +               if (time_after(jiffies, timeout)) {
> +                       dev_err(&mdev->pci_dev->dev,
> +                               "vp_vdpa: fail to reset device\n");
> +                       return -ETIMEDOUT;
> +               }

Any chance to use readx_poll_timeout() here?

Thanks

> +       }
> +
>         if (s & VIRTIO_CONFIG_S_DRIVER_OK)
>                 vp_vdpa_free_irq(vp_vdpa);
>
> --
> 2.23.0
>