STUB_DATA_PAGES
#define STUB_SIZE ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE)
free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
.ss_size = STUB_DATA_PAGES * UM_KERN_PAGE_SIZE,
STUB_DATA_PAGES * UM_KERN_PAGE_SIZE,