在 2021/6/23 下午1:50, Yongji Xie 写道:
On Wed, Jun 23, 2021 at 11:31 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
在 2021/6/22 下午4:14, Yongji Xie 写道:
On Tue, Jun 22, 2021 at 3:50 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
在 2021/6/22 下午3:22, Yongji Xie 写道:
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@xxxxxxxxxxxxx/
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
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