An example physical memory layout (VisionFive v2 SBC):
```
Physical memory chunk(s):
0x40000000 - 0x23fffffff, 8192 MB (2097152 pages)
Excluded memory regions:
0x40000000 - 0x401fffff, 2 MB ( 512 pages) NoAlloc NoDump
0xf6800000 - 0xf961bfff, 46 MB ( 11804 pages) NoAlloc
```
And the corresponding DMAP section of `vm.pmap.kernel_maps`:
```
Direct map:
0xffffffd000200000-0xffffffd200000000 rw-s- PMA 7 511 0
```
...reflecting the 8GB of memory, with the 2MB "NoDump" section excluded from the mapping (7*1GB + 511*2MB).
I intend to perform some more exhaustive testing of the different edge-cases we might encounter.