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

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Date:   Fri, 22 Mar 2019 06:21:27 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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

> 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?

> -#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?

> +#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.

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