Re: [PATCH v6 05/12] mm: HUGE_VMAP arch support cleanup

Andrew Morton
2020-08-21T20:14:25Z

On Sat, 22 Aug 2020 01:12:09 +1000 Nicholas Piggin <npiggin@gmail.com> wrote:

> This changes the awkward approach where architectures provide init
> functions to determine which levels they can provide large mappings for,
> to one where the arch is queried for each call.
>
> This removes code and indirection, and allows constant-folding of dead
> code for unsupported levels.
>
> This also adds a prot argument to the arch query. This is unused
> currently but could help with some architectures (e.g., some powerpc
> processors can't map uncacheable memory with large pages).
>
> --- a/arch/arm64/include/asm/vmalloc.h
> +++ b/arch/arm64/include/asm/vmalloc.h
> @@ -1,4 +1,12 @@
> #ifndef _ASM_ARM64_VMALLOC_H
> #define _ASM_ARM64_VMALLOC_H
>
> +#include <asm/page.h>
> +
> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> +bool arch_vmap_p4d_supported(pgprot_t prot);
> +bool arch_vmap_pud_supported(pgprot_t prot);
> +bool arch_vmap_pmd_supported(pgprot_t prot);
> +#endif

Moving these out of generic code and into multiple arch headers is
unfortunate. Can we leave them in include/linux/somewhere? And remove
the ifdefs, if so inclined - they just move the build error from
link-time to compile-time, and such an error shouldn't occur!