linux-kernel - Re: [RFC V2 01/10] mm/mmap: Dynamically initialize protection

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Message-ID: <20210805170318.GB6719@arm.com>
Date:   Thu, 5 Aug 2021 18:03:18 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        suzuki.poulose@....com, mark.rutland@....com, will@...nel.org,
        maz@...nel.org, james.morse@....com, steven.price@....com
Subject: Re: [RFC V2 01/10] mm/mmap: Dynamically initialize protection_map[]

On Mon, Jul 26, 2021 at 12:07:16PM +0530, Anshuman Khandual wrote:
> The protection_map[] elements (__PXXX and __SXXX) might sometimes contain
> runtime variables in certain platforms like arm64 preventing a successful
> build because of the current static initialization. So it just defers the
> initialization until mmmap_init() via a new helper init_protection_map().
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  mm/mmap.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index ca54d36..a95b078 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -100,10 +100,7 @@ static void unmap_region(struct mm_struct *mm,
>   *								w: (no) no
>   *								x: (yes) yes
>   */
> -pgprot_t protection_map[16] __ro_after_init = {
> -	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
> -	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
> -};
> +pgprot_t protection_map[16] __ro_after_init;

Mips, x86, sparc, arm32, m68k all adjust protection_map[] during boot.
Could we do something similar here and avoid changing the generic code?

-- 
Catalin