KERN_VIRT_SIZE
#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 2)
#define KERN_IO_START (KERN_VIRT_START + (KERN_VIRT_SIZE >> 1))
#define KERN_IO_SIZE (KERN_VIRT_SIZE >> 2)
((x) >= PAGE_OFFSET && (!IS_ENABLED(CONFIG_64BIT) || (x) < PAGE_OFFSET + KERN_VIRT_SIZE))
#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
memory_limit = KERN_VIRT_SIZE;
max_mapped_addr = __pa(PAGE_OFFSET) + KERN_VIRT_SIZE;