linux-kernel - Re: [PATCH v4 03/12] mm: Reserve asm-generic prot flag 0x10 for arch use

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Date:   Thu, 12 Dec 2019 10:48:32 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Will Deacon <will@...nel.org>, Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Marc Zyngier <maz@...nel.org>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>, Andrew Jones <drjones@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Florian Weimer <fweimer@...hat.com>,
        Sudakshina Das <sudi.das@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v4 03/12] mm: Reserve asm-generic prot flag 0x10 for arch
 use

On Wed, Dec 11, 2019 at 03:41:57PM +0000, Mark Brown wrote:
> From: Dave Martin <Dave.Martin@....com>
> 
> The asm-generic mman definitions are used by a few architectures
> that also define an arch-specific PROT flag with value 0x10.  This
> currently applies to sparc and powerpc, and arm64 will soon join
> in.
> 
> To help future maintainers, document the use of this flag in the
> asm-generic header too.
> 
> Signed-off-by: Dave Martin <Dave.Martin@....com>
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  include/uapi/asm-generic/mman-common.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> index c160a5354eb6..81442d2aaecb 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -11,6 +11,7 @@
>  #define PROT_WRITE	0x2		/* page can be written */
>  #define PROT_EXEC	0x4		/* page can be executed */
>  #define PROT_SEM	0x8		/* page may be used for atomic ops */
> + /*			0x10		   reserved for arch-specific use */
>  #define PROT_NONE	0x0		/* page can not be accessed */
>  #define PROT_GROWSDOWN	0x01000000	/* mprotect flag: extend change to start of growsdown vma */
>  #define PROT_GROWSUP	0x02000000	/* mprotect flag: extend change to end of growsup vma */

Since the BTI will likely be merged before the MTE series, please
consider reserving 0x20 as well. The updated patch, acked by Arnd:

https://lore.kernel.org/linux-arm-kernel/20191211184027.20130-2-catalin.marinas@arm.com/

-- 
Catalin