On Wed 25-03-20 17:12:14, glider@xxxxxxxxxx wrote:
> This flag is to be used by KMSAN runtime to mark that newly created
> memory pages don't need KMSAN metadata backing them.
I really dislike an idea of the gfp flag. If you need some form of
exclusion for kmsan allocations then follow the pattern of memalloc_no{fs,io}_{save,restore}
History tells us that single usecase gfp flags are too tempting to abuse
and using incorrectly.
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> To: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
>
> ---
> We can't decide what to do here:
> - do we need to conditionally define ___GFP_NO_KMSAN_SHADOW depending on
> CONFIG_KMSAN like LOCKDEP does?
> - if KMSAN is defined, and LOCKDEP is not, do we want to "compactify" the GFP
> bits?
>
> Change-Id: If5d0352fd5711ad103328e2c185eb885e826423a
> ---
> include/linux/gfp.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index be2754841369e..e1ab42b5e9ce2 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -44,6 +44,7 @@ struct vm_area_struct;
> #else
> #define ___GFP_NOLOCKDEP 0
> #endif
> +#define ___GFP_NO_KMSAN_SHADOW 0x1000000u
> /* If the above are modified, __GFP_BITS_SHIFT may need updating */
>
> /*
> @@ -212,12 +213,13 @@ struct vm_area_struct;
> #define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
> #define __GFP_COMP ((__force gfp_t)___GFP_COMP)
> #define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
> +#define __GFP_NO_KMSAN_SHADOW ((__force gfp_t)___GFP_NO_KMSAN_SHADOW)
>
> /* Disable lockdep for GFP context tracking */
> #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
>
> /* Room for N __GFP_FOO bits */
> -#define __GFP_BITS_SHIFT (23 + IS_ENABLED(CONFIG_LOCKDEP))
> +#define __GFP_BITS_SHIFT (25)
> #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
>
> /**
> --
> 2.25.1.696.g5e7596f4ac-goog
>
--
Michal Hocko
SUSE Labs
