VTTBR_VMID_SHIFT
#define VTTBR_VMID_MASK(size) (_AT(u64, (1 << size) - 1) << VTTBR_VMID_SHIFT)
vmid_field = atomic64_read(&vmid->id) << VTTBR_VMID_SHIFT;
VTTBR_VMID_SHIFT;