44f06ae57d
its PVO to map physical address 0 instead of kernelstart. This fixes a situation in which a user process could attempt to return this address via KVM, have it fault while being modified, and then panic the kernel because (a) it is supposed to map a valid address and (b) it lies in the no-fault region between VM_MIN_KERNEL_ADDRESS and virtual_avail. While here, move msgbuf and dpcpu make into regular KVA space for consistency with other implementations.