On Fri, Feb 21, 2025 at 7:42 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> Hongyu reported a hang on kexec in a VM. QEMU reported invalid memory
> accesses during the hang.
>
> Invalid read at addr 0x102877002, size 2, region '(null)', reason: rejected
> Invalid write at addr 0x102877A44, size 2, region '(null)', reason: rejected
> ...
>
> It was traced down to virtio-console. Kexec works fine if virtio-console
> is not in use.
>
> The issue is that virtio-console continues to write to the MMIO even after
> underlying virtio-pci device is reset.
Some of my questions were not answered so I need to post them again.
Do we need to fix vitio-console?
Note that we've already break the device in virtio_pci_remove():
static void virtio_pci_remove(struct pci_dev *pci_dev)
{
struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
struct device *dev = get_device(&vp_dev->vdev.dev);
/*
* Device is marked broken on surprise removal so that virtio upper
* layers can abort any ongoing operation.
*/
if (!pci_device_is_present(pci_dev))
virtio_break_device(&vp_dev->vdev);
...
>
> Additionally, Eric noticed that IOMMUs are reset before devices, if
> devices are not reset on shutdown they continue to poke at guest memory
> and get errors from the IOMMU. Some devices get wedged then.
>
> The problem can be solved by breaking all virtio devices on virtio
> bus shutdown, then resetting them.
>
> Reported-by: Eric Auger <eauger@xxxxxxxxxx>
> Reported-by: Hongyu Ning <hongyu.ning@xxxxxxxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/virtio/virtio.c | 31 +++++++++++++++++++++++++++++++
> 1 file changed, 31 insertions(+)
>
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index c1cc1157b380..e5b29520d3b2 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -377,6 +377,36 @@ static void virtio_dev_remove(struct device *_d)
> of_node_put(dev->dev.of_node);
> }
>
> +static void virtio_dev_shutdown(struct device *_d)
> +{
> + struct virtio_device *dev = dev_to_virtio(_d);
> + struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
> +
> + /*
> + * Stop accesses to or from the device.
> + * We only need to do it if there's a driver - no accesses otherwise.
> + */
> + if (!drv)
> + return;
> +
> + /*
> + * Some devices get wedged if you kick them after they are
> + * reset. Mark all vqs as broken to make sure we don't.
> + */
> + virtio_break_device(dev);
> + /*
> + * The below virtio_synchronize_cbs() guarantees that any interrupt
> + * for this line arriving after virtio_synchronize_vqs() has completed
> + * is guaranteed to see vq->broken as true.
> + */
> + virtio_synchronize_cbs(dev);
This looks like a partial re-introduction of the hardening work, but
the ccw part is still in-completed e.g the synchronization requires a
read_lock() and depends on CONFIG_VIRTIO_HARDEN_NOTIFICATION (which is
marked as broken now).
Should it better to
1) fix the virtio-console
2) simply rest in shutdown
3) wait for the hardening work to be done in the future?
Thanks
> + /*
> + * As IOMMUs are reset on shutdown, this will block device access to memory.
> + * Some devices get wedged if this happens, so reset to make sure it does not.
> + */
> + dev->config->reset(dev);
> +}
> +
> static const struct bus_type virtio_bus = {
> .name = "virtio",
> .match = virtio_dev_match,
> @@ -384,6 +414,7 @@ static const struct bus_type virtio_bus = {
> .uevent = virtio_uevent,
> .probe = virtio_dev_probe,
> .remove = virtio_dev_remove,
> + .shutdown = virtio_dev_shutdown,
> };
>
> int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
> --
> MST
>
