hv_mach_desc
hv_mach_desc((paddr_t)NULL, &len); /* Trick to get actual length */
hv_rc = hv_mach_desc(pa, &len);
int64_t hv_mach_desc(paddr_t buffer, psize_t *length);
hv_mach_desc(0, &len);
err = hv_mach_desc(pa, &len);