Re: [RFC PATCH v4 2/9] tools headers: Add a macro to get HUGETLB page sizes for mmap

[Andrew Jones]

On Tue, Mar 02, 2021 at 08:57:44PM +0800, Yanan Wang wrote:
> We know that if a system supports multiple hugetlb page sizes,
> the desired hugetlb page size can be specified in bits [26:31]
> of the flag arguments. The value in these 6 bits will be the
> shift of each hugetlb page size.
> 
> So add a macro to get the page size shift and then calculate the
> corresponding hugetlb page size, using flag x.
> 
> Cc: Ben Gardon <bgardon@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Suggested-by: Ben Gardon <bgardon@xxxxxxxxxx>
> Signed-off-by: Yanan Wang <wangyanan55@xxxxxxxxxx>
> Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
>  include/uapi/linux/mman.h       | 2 ++
>  tools/include/uapi/linux/mman.h | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
> index f55bc680b5b0..8bd41128a0ee 100644
> --- a/include/uapi/linux/mman.h
> +++ b/include/uapi/linux/mman.h
> @@ -41,4 +41,6 @@
>  #define MAP_HUGE_2GB	HUGETLB_FLAG_ENCODE_2GB
>  #define MAP_HUGE_16GB	HUGETLB_FLAG_ENCODE_16GB
>  
> +#define MAP_HUGE_PAGE_SIZE(x) (1 << ((x >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK))

Needs to be '1ULL' to avoid shift overflow when given MAP_HUGE_16GB.

Thanks,
drew

> +
>  #endif /* _UAPI_LINUX_MMAN_H */
> diff --git a/tools/include/uapi/linux/mman.h b/tools/include/uapi/linux/mman.h
> index f55bc680b5b0..8bd41128a0ee 100644
> --- a/tools/include/uapi/linux/mman.h
> +++ b/tools/include/uapi/linux/mman.h
> @@ -41,4 +41,6 @@
>  #define MAP_HUGE_2GB	HUGETLB_FLAG_ENCODE_2GB
>  #define MAP_HUGE_16GB	HUGETLB_FLAG_ENCODE_16GB
>  
> +#define MAP_HUGE_PAGE_SIZE(x) (1 << ((x >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK))
> +
>  #endif /* _UAPI_LINUX_MMAN_H */
> -- 
> 2.23.0
>