linux-kernel - Re: [PATCH v3 1/2] arm64: refactor the rodata=xxx

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Message-ID: <CAMj1kXFJhFfhy=Gwm=QrdN6XPUd=7SKNKFBF_Z4eQ30r509BCg@mail.gmail.com>
Date: Tue, 10 Dec 2024 08:21:56 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Huang Shijie <shijie@...amperecomputing.com>, catalin.marinas@....com, will@...nel.org, 
	corbet@....net, patches@...erecomputing.com, cl@...ux.com, 
	akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org, 
	xiongwei.song@...driver.com, inux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/2] arm64: refactor the rodata=xxx

On Tue, 10 Dec 2024 at 08:17, Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
...
>
> Reformatted and cleaned up the above comment a bit but feel free to
> improve it further.
>
> /*
>  * rodata=on (default)
>  *
>  *    This applies read-only attributes to VM areas and to the linear
>  *    alias of the backing pages as well. This prevents code or read-
>  *    only data from being modified (inadvertently or intentionally),
>  *    via another mapping for the same memory page.
>  *
>  *    But this might cause linear map region to be mapped down to base
>  *    pages, which may adversely affect performance in some cases.
>  *
>  * rodata=off
>  *
>  *    This provides more block mappings and contiguous hints for linear
>  *    map region which would minimize TLB footprint. This also leaves
>  *    read-only kernel memory writable for debugging.
>  *
>  * rodata=noalias
>  *
>  *    This provides more block mappings and contiguous hints for linear
>  *    map region which would minimize TLB footprint. Linear aliases of
>  *    pages belonging to read-only mappings in vmalloc region are also
>  *    marked as read-only.
>

If linear aliases are marked as read-only, how does 'noalias' differ from 'on'?