EMM386 and VDS: not quite working

The other day I set out to solve a seemingly simple problem: With a DOS extended application, lock down memory buffers using DPMI and use them for bus-mastering (BusLogic SCSI HBA, though the exact device model isn't really relevant to the problem).

Now, DPMI does not allow querying the physical address of a memory region, although it does have provisions for mapping a given physical memory area. But that doesn't help here-mapping physical memory is useful for framebuffers where a device memory needs to be mapped so that an application can access it. In my case, I needed the opposite, allowing a bus-mastering device to use already-allocated system memory.

I think I may have understood some of these words.