[syslinux] UEFI memdisk freeze

[bear]

Hi all,
My computer is booted with UEFI and Grub2. I tried to load VHD files
with memdisk and boot from there. memdisk is extracted from
'bios/memdisk' in syslinux 6.03 zip file.
In Grub2, I executed:

linux16 /memdisk harddisk
initrd16 /Win10.vhd

Then the system frozen at 'initrd16' line.
The VHD file is 8192MB, fixed image. I also tried to boot a small
floppy disk (FreeDOS), and no error reported from Grub2 or memdisk
side.

Is there anything wrong with my steps? How to properly load an fixed
VHD image to ram disk and boot it?