VHOST_PAGE_SIZE
u64 a = addr / VHOST_PAGE_SIZE / 8;
(sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8);
u64 write_page = write_address / VHOST_PAGE_SIZE;
write_length += write_address % VHOST_PAGE_SIZE;
if (write_length <= VHOST_PAGE_SIZE)
write_length -= VHOST_PAGE_SIZE;