Jason Wang
2021-Jun-24 03:34 UTC
[PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace
? 2021/6/23 ??1:50, Yongji Xie ??:> On Wed, Jun 23, 2021 at 11:31 AM Jason Wang <jasowang at redhat.com> wrote: >> >> ? 2021/6/22 ??4:14, Yongji Xie ??: >>> On Tue, Jun 22, 2021 at 3:50 PM Jason Wang <jasowang at redhat.com> wrote: >>>> ? 2021/6/22 ??3:22, Yongji Xie ??: >>>>>> We need fix a way to propagate the error to the userspace. >>>>>> >>>>>> E.g if we want to stop the deivce, we will delay the status reset until >>>>>> we get respose from the userspace? >>>>>> >>>>> I didn't get how to delay the status reset. And should it be a DoS >>>>> that we want to fix if the userspace doesn't give a response forever? >>>> You're right. So let's make set_status() can fail first, then propagate >>>> its failure via VHOST_VDPA_SET_STATUS. >>>> >>> OK. So we only need to propagate the failure in the vhost-vdpa case, right? >> >> I think not, we need to deal with the reset for virtio as well: >> >> E.g in register_virtio_devices(), we have: >> >> /* 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); >> >> We probably need to make reset can fail and then fail the >> register_virtio_device() as well. >> > OK, looks like virtio_add_status() and virtio_device_ready()[1] should > be also modified if we need to propagate the failure in the > virtio-vdpa case. Or do we only need to care about the reset case? > > [1] https://lore.kernel.org/lkml/20210517093428.670-1-xieyongji at bytedance.com/My understanding is DRIVER_OK is not something that needs to be validated: " DRIVER_OK (4) Indicates that the driver is set up and ready to drive the device. " Since the spec doesn't require to re-read the and check if DRIVER_OK is set in 3.1.1 Driver Requirements: Device Initialization. It's more about "telling the device that driver is ready." But we don have some status bit that requires the synchronization with the device. 1) FEATURES_OK, spec requires to re-read the status bit to check whether or it it was set by the device: " Re-read device status to ensure the FEATURES_OK bit is still set: otherwise, the device does not support our subset of features and the device is unusable. " This is useful for some device which can only support a subset of the features. E.g a device that can only work for packed virtqueue. This means the current design of set_features won't work, we need either: 1a) relay the set_features request to userspace or 1b) introduce a mandated_device_features during device creation and validate the driver features during the set_features(), and don't set FEATURES_OK if they don't match. 2) Some transports (PCI) requires to re-read the status to ensure the synchronization. " After writing 0 to device_status, the driver MUST wait for a read of device_status to return 0 before reinitializing the device. " So we need to deal with both FEATURES_OK and reset, but probably not DRIVER_OK. Thanks> > Thanks, > Yongji >