[PATCH] vp_vdpa: harden the logic of set status

[Longpeng(Mike)]

From: Longpeng <longpeng2@xxxxxxxxxx>

1. We should not set status to 0 when invoking vp_vdpa_set_status().

2. The driver MUST wait for a read of device_status to return 0 before
   reinitializing the device.

Signed-off-by: Longpeng <longpeng2@xxxxxxxxxx>
---
 drivers/vdpa/virtio_pci/vp_vdpa.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
index d448db0c4de3..d35fac5cde11 100644
--- a/drivers/vdpa/virtio_pci/vp_vdpa.c
+++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
@@ -212,8 +212,12 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
 {
 	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);
+	u8 s;
+
+	/* We should never be setting status to 0. */
+	BUG_ON(status == 0);
 
+	s = vp_vdpa_get_status(vdpa);
 	if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
 	    !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
 		vp_vdpa_request_irq(vp_vdpa);
@@ -229,6 +233,11 @@ static int vp_vdpa_reset(struct vdpa_device *vdpa)
 	u8 s = vp_vdpa_get_status(vdpa);
 
 	vp_modern_set_status(mdev, 0);
+	/* After writing 0 to device_status, the driver MUST wait for a read of
+	 * device_status to return 0 before reinitializing the device.
+	 */
+	while (vp_modern_get_status(mdev))
+		msleep(1);
 
 	if (s & VIRTIO_CONFIG_S_DRIVER_OK)
 		vp_vdpa_free_irq(vp_vdpa);
-- 
2.23.0