vmsplice returned "bad address"

[Teoh Choon Zone]

I have a driver which will dma_alloc a CMA region and return the address to
my user space program, the program then will mmap /dev/mem according to the
address offset. I was trying to vmsplice and splice it into my socket
buffer, but the vmsplice always return "bad address". Anybody knows why? I
attach my user space code for your perusal.
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