Hello Hanna, On Wed, Jul 10, 2024 at 01:23:10PM +0200, Hanna Czenczek wrote: > Requiring `vhost_started` to be true for resetting vhost devices in > `virtio_reset()` seems like the wrong condition: Most importantly, the > preceding `virtio_set_status(vdev, 0)` call will (for vhost devices) end > up in `vhost_dev_stop()` (through vhost devices' `.set_status` > implementations), setting `vdev->vhost_started = false`. Therefore, the > gated `vhost_reset_device()` call is unreachable. > > `vhost_started` is not documented, so it is hard to say what exactly it > is supposed to mean, but judging from the fact that `vhost_dev_start()` > sets it and `vhost_dev_stop()` clears it, it seems like it indicates > whether there is a vhost back-end, and whether that back-end is > currently running and processing virtio requests. > > Making a reset conditional on whether the vhost back-end is processing > virtio requests seems wrong; in fact, it is probably better to reset it > only when it is not currently processing requests, which is exactly the > current order of operations in `virtio_reset()`: First, the back-end is > stopped through `virtio_set_status(vdev, 0)`, then we want to send a > reset. > > Therefore, we should drop the `vhost_started` condition, but in its > stead we then have to verify that we can indeed send a reset to this > vhost device, by not just checking `k->get_vhost != NULL` (introduced by > commit 95e1019a4a9), but also that the vhost back-end is connected > (`hdev = k->get_vhost(); hdev != NULL && hdev->vhost_ops != NULL`). >
I am not a native speaker but I think the commit message could be rephrased to make it clear. This is a minor comment so feel free to ignore it: Before `virtio_reset()` is invoked, `virtio_set_status(vdev, 0)` for vhost devices ends up setting `vhost_stared` to false thus resulting in `vhost_reset_device()` being never reached during a reset. `vhost_started` is not documented, however, from `vhost_dev_start()` and `vhost_dev_stop()`, it seems indicating that there is a vhost back-end and that the back-end is running and processing virtio requests. Resetting should not rely on whether the vhost back-end is processing virtio requests, instead, reset must happen if there is no processing request. This is what `virtio_reset()` does, it first stops the backend and then sends the reset. To trigger a reset, this commit drops the `vhost_started` condition and checks that the device is running (introduced by 95e1019a4a9) but also that the vhost back-end is connected so it is possible to send a reset to the vhost device. Matias
