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

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Date:   Fri, 12 Mar 2021 12:14:56 +0100
From:   Andrew Jones <drjones@...hat.com>
To:     Yanan Wang <wangyanan55@...wei.com>
Cc:     kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Ben Gardon <bgardon@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Peter Xu <peterx@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        wanghaibin.wang@...wei.com, yezengruan@...wei.com,
        yuzenghui@...wei.com
Subject: Re: [RFC PATCH v4 2/9] tools headers: Add a macro to get HUGETLB
 page sizes for mmap

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@...gle.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Michael Kerrisk <mtk.manpages@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Suggested-by: Ben Gardon <bgardon@...gle.com>
> Signed-off-by: Yanan Wang <wangyanan55@...wei.com>
> Reviewed-by: Ben Gardon <bgardon@...gle.com>
> ---
>  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
>