linux-kernel - Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits

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Message-ID: <87zfol468z.fsf@mail.lhotse>
Date: Fri, 06 Sep 2024 16:59:40 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Charlie Jenkins <charlie@...osinc.com>, Arnd Bergmann <arnd@...db.de>,
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Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
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 Charlie Jenkins <charlie@...osinc.com>
Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to
 47 bits

Charlie Jenkins <charlie@...osinc.com> writes:
> Create a personality flag ADDR_LIMIT_47BIT to support applications
> that wish to transition from running in environments that support at
> most 47-bit VAs to environments that support larger VAs. This
> personality can be set to cause all allocations to be below the 47-bit
> boundary. Using MAP_FIXED with mmap() will bypass this restriction.
>
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> ---
>  include/uapi/linux/personality.h | 1 +
>  mm/mmap.c                        | 3 +++
>  2 files changed, 4 insertions(+)
>
> diff --git a/include/uapi/linux/personality.h b/include/uapi/linux/personality.h
> index 49796b7756af..cd3b8c154d9b 100644
> --- a/include/uapi/linux/personality.h
> +++ b/include/uapi/linux/personality.h
> @@ -22,6 +22,7 @@ enum {
>  	WHOLE_SECONDS =		0x2000000,
>  	STICKY_TIMEOUTS	=	0x4000000,
>  	ADDR_LIMIT_3GB = 	0x8000000,
> +	ADDR_LIMIT_47BIT = 	0x10000000,
>  };

I wonder if ADDR_LIMIT_128T would be clearer?

Have you looked at writing an update for the personality(2) man page? :)

cheers