[PATCH 3/5] arm64: mm: use a compile time constant for vabits_actual when possible

[Will Deacon]

On Wed, Mar 10, 2021 at 06:15:13PM +0100, Ard Biesheuvel wrote:
> The size of the kernel VA space is a compile time constant unless the
> kernel is built to support 52-bit virtual addressing, which today is
> only supported on 64k page size kernels (although this has recently
> changed in the architecture).
> 
> This means that in many configurations, vabits_actual can never deviate
> from its build time default, making it rather pointless to carry this
> value in a variable. So use a compile time constant for vabits_actual
> unless it can really assume different values.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  arch/arm64/include/asm/memory.h |  4 ++++
>  arch/arm64/kernel/head.S        | 12 ++++++------
>  arch/arm64/mm/mmu.c             |  2 ++
>  3 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index c759faf7a1ff..501c5c87ec0a 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -179,7 +179,11 @@
>  #include <linux/types.h>
>  #include <asm/bug.h>
>  
> +#ifdef CONFIG_ARM64_VA_BITS_52
>  extern u64			vabits_actual;
> +#else
> +#define vabits_actual		((u64)VA_BITS)
> +#endif

Maybe we should have VA_BITS_MIN, VA_BITS and VA_BITS_MAX instead of
the current VA_BITS_MIN, VA_BITS and vabits_actual? The current naming is
definitely a source of confusion for me.

Will