cpu_pabits
#define VMEMMAP_SIZE (sizeof(struct page) * (1UL << (cpu_pabits + 1 - PAGE_SHIFT)))
c->pabits = cpu_pabits;
cpu_pabits + 1, cpu_vabits + 1);
return !(((pfn << PAGE_SHIFT) + size) & ~(GENMASK_ULL(cpu_pabits, 0)));