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

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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

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