On 2020/12/23 下午6:59, Yongji Xie wrote:

On Wed, Dec 23, 2020 at 2:38 PM Jason Wang [off-list ref] wrote:

quoted

On 2020/12/22 下午10:52, Xie Yongji wrote:

quoted

This series introduces a framework, which can be used to implement
vDPA Devices in a userspace program. The work consist of two parts:
control path forwarding and data path offloading.

In the control path, the VDUSE driver will make use of message
mechnism to forward the config operation from vdpa bus driver
to userspace. Userspace can use read()/write() to receive/reply
those control messages.

In the data path, the core is mapping dma buffer into VDUSE
daemon's address space, which can be implemented in different ways
depending on the vdpa bus to which the vDPA device is attached.

In virtio-vdpa case, we implements a MMU-based on-chip IOMMU driver with
bounce-buffering mechanism to achieve that.

Rethink about the bounce buffer stuffs. I wonder instead of using kernel
pages with mmap(), how about just use userspace pages like what vhost did?

It means we need a worker to do bouncing but we don't need to care about
annoying stuffs like page reclaiming?

Now the I/O bouncing is done in the streaming DMA mapping routines
which can be called from interrupt context. If we put this into a
kworker, that means we need to synchronize with a kworker in an
interrupt context. I think it can't work.

We just need to make sure the buffer is ready before the user is trying 
to access them.

But I admit it would be tricky (require shadow virtqueue etc) which is 
probably not a good idea.

Thanks

Thanks,
Yongji