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

[Stefano Garzarella]

On Tue, Dec 06, 2022 at 10:13:21AM +0800, Longpeng(Mike) wrote:
> From: Longpeng <longpeng2@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
> 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 */

What about moving this define on top of this file?
Near the other macro.

And I would use TIMEOUT entirely.

> +
> 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

I think we can refer to the lates v1.2 (the section should be the same).

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

The rest LGTM!

Thanks,
Stefano