UPPER_SZ
for (uintptr_t gpa = UPPER_OFF; gpa < UPPER_OFF + UPPER_SZ; gpa++) {
res = vm_munmap_memseg(ctx, UPPER_OFF, UPPER_SZ);
#define TOTAL_SZ (LOWER_SZ + UPPER_SZ)
res = alloc_memseg(ctx, MSEG_HIGH, UPPER_SZ, "mseg_high");
res = vm_mmap_memseg(ctx, UPPER_OFF, MSEG_HIGH, 0, UPPER_SZ, PROT_ALL);