On Wed, May 11 2022, Jason Wang <jasowang@xxxxxxxxxx> wrote: > On Tue, May 10, 2022 at 7:32 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: >> >> On Sat, May 07, 2022 at 03:19:53PM +0800, Jason Wang wrote: >> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h >> > index d8a2340f928e..23f1694cdbd5 100644 >> > --- a/include/linux/virtio_config.h >> > +++ b/include/linux/virtio_config.h >> > @@ -256,6 +256,18 @@ void virtio_device_ready(struct virtio_device *dev) >> > unsigned status = dev->config->get_status(dev); >> > >> > BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK); >> > + >> > + /* >> > + * The virtio_synchronize_cbs() makes sure vring_interrupt() >> > + * will see the driver specific setup if it sees vq->broken >> > + * as false. >> > + */ >> > + virtio_synchronize_cbs(dev); >> >> since you mention vq->broken above, maybe add >> "set vq->broken to false" > > Ok. > >> >> > + __virtio_unbreak_device(dev); >> > + /* >> > + * The transport is expected ensure the visibility of >> >> to ensure > > Will fix. > >> >> > + * vq->broken >> >> let's add: "visibility by vq callbacks" > > Sure. > >> >> > before setting VIRTIO_CONFIG_S_DRIVER_OK. >> > + */ >> >> >> Can I see some analysis of existing transports showing >> this is actually the case for them? > > Yes. > >> And maybe add a comment near set_status to document the >> requirement. > > For PCI and MMIO, we can quote the memory-barriers.txt or explain that > wmb() is not needed before the MMIO writel(). > For CCW, it looks not obvious, it looks to me the IO was submitted via > __ssch() which has an inline assembly. Cornelia and Hali, could you > help me to understand if and how did virtio_ccw_set_status() can > ensure the visibility of the previous driver setup and vq->broken > here? I'm not sure I completely understand the question here, but let me try: virtio_ccw_set_status() uses a channel command to set the status, with the interesting stuff done inside ccw_io_helper(). That function - takes the subchannel lock, disabling interrupts - does the ssch; this instruction will fail if there's already another I/O in progress, or an interrupt is pending for the subchannel; on success, it is guaranteed that we'll get an interrupt eventually - unlock the subchannel, and wait for the interupt handler to eventually process the interrupt, so I guess it should see the vq->broken value? If the I/O fails, virtio_ccw_set_status() will revert its internal status to the old value. > > Thanks > >> >> > dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK); >> > } _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
