Re: [PATCH] x86/percpu: Use __force to cast from __percpu address space

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, May 14, 2024 at 10:39:18AM +0200, Uros Bizjak wrote:
> commit a55c1fdad5f61b4bfe42319694b23671a758cb28 upstream.
> 
> Fix Sparse warning when casting from __percpu address space by using
> __force in the cast. x86 named address spaces are not considered to
> be subspaces of the generic (flat) address space, so explicit casts
> are required to convert pointers between these address spaces and the
> generic address space (the application should cast to uintptr_t and
> apply the segment base offset). The cast to uintptr_t removes
> __percpu address space tag and Sparse reports:
> 
>   warning: cast removes address space '__percpu' of expression
> 
> Use __force to inform Sparse that the cast is intentional.

Why is a fix for sparse required for stable kernels?

> The patch deviates from upstream commit due to the unification of
> arch_raw_cpu_ptr() defines in the commit:
> 
>   4e5b0e8003df ("x86/percpu: Unify arch_raw_cpu_ptr() defines").
> 
> Fixes: 9a462b9eafa6 ("x86/percpu: Use compiler segment prefix qualifier")
> Reported-by: Charlemagne Lasse <charlemagnelasse@gmail.com>
> Closes: https://lore.kernel.org/lkml/CAFGhKbzev7W4aHwhFPWwMZQEHenVgZUj7=aunFieVqZg3mt14A@mail.gmail.com/
> Cc: stable@vger.kernel.org # v6.8
> Link: https://lore.kernel.org/r/20240402175058.52649-1-ubizjak@gmail.com
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> ---
>  arch/x86/include/asm/percpu.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

And also, what kernel version(s) is this for?

I don't see this in any released kernels yet either, is that
intentional?

thanks,

greg k-h