procinit() and map them high up (below TRAMPOLNE) with an empty mapping below each stack. Never free a kernel stack. Another way would be to allocate and map them dynamically, but then we need to reload page table when switching processes in scheduler() and/or have a kernel pagetable per proc (if we want k->stack to be the same virtual address in each process). One gotcha: kernel addresses are not equal to physical addresses for stack addresses. A stack address must be translated if we need its physical address (e.g., virtio passes a stack address to the disk).