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SubjectRe: [PATCH v2 1/3] kasan, arm64: use ARCH_SLAB_MINALIGN instead of manual aligning
On Wed,  2 Jan 2019 18:36:06 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:

> Instead of changing cache->align to be aligned to KASAN_SHADOW_SCALE_SIZE
> in kasan_cache_create() we can reuse the ARCH_SLAB_MINALIGN macro.
>
> ...
>
> --- a/arch/arm64/include/asm/kasan.h
> +++ b/arch/arm64/include/asm/kasan.h
> @@ -36,6 +36,10 @@
> #define KASAN_SHADOW_OFFSET (KASAN_SHADOW_END - (1ULL << \
> (64 - KASAN_SHADOW_SCALE_SHIFT)))
>
> +#ifdef CONFIG_KASAN_SW_TAGS
> +#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT)
> +#endif
> +
> void kasan_init(void);
> void kasan_copy_shadow(pgd_t *pgdir);
> asmlinkage void kasan_early_init(void);
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 11b45f7ae405..d87f913ab4e8 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -16,6 +16,7 @@
> #include <linux/overflow.h>
> #include <linux/types.h>
> #include <linux/workqueue.h>
> +#include <linux/kasan.h>
>

This still seems unadvisable. Like other architectures, arm defines
ARCH_SLAB_MINALIGN in arch/arm/include/asm/cache.h.
arch/arm/include/asm64/cache.h doesn't define ARCH_SLAB_MINALIGN
afaict.

If arch/arm/include/asm64/cache.h later gets a definition of
ARCH_SLAB_MINALIGN then we again face the risk that different .c files
will see different values of ARCH_SLAB_MINALIGN depending on which
headers they include.

So what to say about this? The architecture's ARCH_SLAB_MINALIGN
should be defined in the architecture's cache.h, end of story. Not in
slab.h, not in kasan.h.


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