[PATCH 2/2] virtio_pci_modern: avoid infinite loop in vp_reset() on invalid status

[Abhin Parekadan Jose <abhinjoses@gmail.com>]

vp_reset() polls device_status in a tight loop, waiting for it to read
back as 0 after the reset write. device_status is read via MMIO from
the common configuration structure, which requires the PCI_COMMAND
Memory Space Enable bit to be set. If that bit is cleared while the
device is bound -- e.g. by writing 0x0000 to PCI_COMMAND (config space
offset 4) -- the MMIO read no longer reaches the device and returns
the bus's synthesized all-ones response instead. Since that value can
never legitimately clear to 0, the loop spins forever and hangs the
caller.

Use VIRTIO_STATUS_ERROR() to recognize such values and bail out of the
poll loop instead of looping indefinitely.

Signed-off-by: Abhin Parekadan Jose <abhinjoses@gmail.com>
---
 drivers/virtio/virtio_pci_modern.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index 6d8ae2a6a8ca..209fa3b36c90 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -547,6 +547,7 @@ static void vp_reset(struct virtio_device *vdev)
 {
 	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 	struct virtio_pci_modern_device *mdev = &vp_dev->mdev;
+	u8 status;
 
 	/* 0 status means a reset. */
 	vp_modern_set_status(mdev, 0);
@@ -555,8 +556,11 @@ static void vp_reset(struct virtio_device *vdev)
 	 * This will flush out the status write, and flush in device writes,
 	 * including MSI-X interrupts, if any.
 	 */
-	while (vp_modern_get_status(mdev))
+	while ((status = vp_modern_get_status(mdev))) {
+		if (VIRTIO_STATUS_ERROR(status))
+			break;
 		msleep(1);
+	}
 
 	vp_modern_avq_cleanup(vdev);
 
-- 
2.51.1