On 24/08/2017 13:07, Cornelia Huck wrote:
On Wed, 23 Aug 2017 18:33:02 +0200
Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
Reseting a device can sometime fail, even a virtual device.
If the device is not reseted after a while the driver should
abandon the retries.
This is the change proposed for the modern virtio_pci.
More generally, when this happens,the virtio driver can set the
VIRTIO_CONFIG_S_FAILED status flag to advertise the caller.
The virtio core can test if the reset was succesful by testing
this flag after a reset.
This behavior is backward compatible with existing drivers.
This behavior seems to me compatible with Virtio-1.0 specifications,
Chapters 2.1 Device Status Field.
There I definitively need your opinion: Is it right?
Will have to double check with the spec.
This patch also lead to another question:
do we care if a device provided by the hypervisor is buggy?
Getting into a hang because of a broken device is not nice, but I'm not
sure we need to plan for this. Have you seen this in the wild?
Yes, with virtio-pci on S390.
Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx>
---
drivers/virtio/virtio.c | 4 ++++
drivers/virtio/virtio_pci_modern.c | 11 ++++++++++-
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 48230a5..6255dc4 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -324,6 +324,8 @@ int register_virtio_device(struct virtio_device *dev)
/* We always start by resetting the device, in case a previous
* driver messed it up. This also tests that code path a little. */
dev->config->reset(dev);
+ if (dev->config->get_status(dev) & VIRTIO_CONFIG_S_FAILED)
+ return -EIO;
/* Acknowledge that we've seen the device. */
virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
@@ -373,6 +375,8 @@ int virtio_device_restore(struct virtio_device *dev)
/* We always start by resetting the device, in case a previous
* driver messed it up. */
dev->config->reset(dev);
+ if (dev->config->get_status(dev) & VIRTIO_CONFIG_S_FAILED)
+ return -EIO;
virtio-ccw prior to rev 2 won't ever see this (as the read command did
not exist then), but this is not really a problem.
/* Acknowledge that we've seen the device. */
virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index 2555d80..bfc5fc1 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -270,6 +270,7 @@ static void vp_set_status(struct virtio_device *vdev, u8 status)
static void vp_reset(struct virtio_device *vdev)
{
struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+ int retry_count = 10;
When you're touching this anyway, it would be a good time to add an
extra blank line :)
Yes, I like blank lines too.
/* 0 status means a reset. */
vp_iowrite8(0, &vp_dev->common->device_status);
/* After writing 0 to device_status, the driver MUST wait for a read of
@@ -277,8 +278,16 @@ 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_ioread8(&vp_dev->common->device_status))
+ while (vp_ioread8(&vp_dev->common->device_status) && retry_count--)
msleep(1);
+ /* If the read did not return 0 before the timeout consider that
+ * the device failed.
+ */
+ if (retry_count <= 0) {
+ virtio_add_status(vdev, VIRTIO_CONFIG_S_FAILED);
+ return;
+ }
+ virtio_add_status(vdev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
Adding ACK here seems wrong?
Exact, I forgot to remove this from a previous test.
I wait a little and post a v2
Thanks for reviewing.
Pierre
/* Flush pending VQ/configuration callbacks. */
vp_synchronize_vectors(vdev);
}
--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany
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