On 2/7/23 17:38, Ming Lei wrote:

Here I meant we can export physical address of request sg from
/dev/ublkb* to userspace, which can program the DMA controller
using exported physical address. With this way, the userspace driver
can submit IO without entering kernel, then with high performance.

Hmm ... security experts might be very unhappy about allowing user space 
software to program iova addresses, PASIDs etc. in DMA controllers 
without having this data verified by the kernel. Additionally, hardware 
designers every now and then propose new device multiplexing mechanisms, 
e.g. scalable IOV which is an alternative for SRIOV. Shouldn't we make 
the kernel deal with these mechanisms instead of user space?

Thanks,

Bart.