linux-kernel - Re: [PATCH 1/4] arm64, mm: Move generic mmap layout functions to mm

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Date:   Sat, 23 Mar 2019 04:18:02 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/4] arm64, mm: Move generic mmap layout functions to mm

On 3/22/19 9:21 AM, Christoph Hellwig wrote:
>> It then introduces a new define ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>> that can be defined by other architectures to benefit from those functions.
> Can you make this a Kconfig option defined in arch/Kconfig or mm/Kconfig
> and selected by the architectures?


Yes, I will do.


>> -#ifndef STACK_RND_MASK
>> -#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))	/* 8MB of VA */
>> -#endif
>> -
>> -static unsigned long randomize_stack_top(unsigned long stack_top)
>> -{
>> -	unsigned long random_variable = 0;
>> -
>> -	if (current->flags & PF_RANDOMIZE) {
>> -		random_variable = get_random_long();
>> -		random_variable &= STACK_RND_MASK;
>> -		random_variable <<= PAGE_SHIFT;
>> -	}
>> -#ifdef CONFIG_STACK_GROWSUP
>> -	return PAGE_ALIGN(stack_top) + random_variable;
>> -#else
>> -	return PAGE_ALIGN(stack_top) - random_variable;
>> -#endif
>> -}
>> -
> Maybe the move of this function can be split into another prep patch,
> as it is only very lightly related?
>
>

Ok, that makes sense.

>> +#if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
>> +	defined(ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
> Not sure if it is wrіtten down somehwere or just convention, but I
> general see cpp defined statements aligned with spaces to the
> one on the previous line.


Ok, I will fix that.


> Except for these nitpicks this looks very nice to me, thanks for doing
> this work!


Thanks :)