Re: [PATCH 1/2] mm: Fix struct page layout on 32-bit systems

On Tue, Apr 20, 2021 at 11:20:19PM +0200, Arnd Bergmann wrote:

In that case, there should be no problem for you.

The main issue is with system calls and ioctls that contain a misaligned
struct member like

struct s {
       u32 a;
       u64 b;
};

Passing this structure by reference from a 32-bit user space application
to a 64-bit kernel with different alignment constraints means that the
kernel has to convert the structure layout. See
compat_ioctl_preallocate() in fs/ioctl.c for one such example.

We've also had this problem with some on-disk structures in the past,
but hopefully people desining those have learnt the lesson by now.