linux-kernel - Re: [PATCH] tile: handle RO_AFTER_INIT

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Message-Id: <20161108071543.GA3528@osiris>
Date:   Tue, 8 Nov 2016 08:15:43 +0100
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Chris Metcalf <cmetcalf@...lanox.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] tile: handle RO_AFTER_INIT_DATA

On Mon, Nov 07, 2016 at 02:50:27PM -0500, Chris Metcalf wrote:
> This is the minimal change to handle RO_AFTER_INIT_DATA.
> The tile architecture already marks RO_DATA as read-only in
> the kernel, so grouping RO_AFTER_INIT_DATA with RO_DATA, as is
> done by default, means the kernel faults in init when it tries
> to write to RO_AFTER_INIT_DATA.  For now, just move it past the
> end of the RODATA section so it is not specially treated.
> ---
> This is just to fix 4.9; I will post a more complete fix shortly
> targeting 4.10.
> 
>  arch/tile/kernel/vmlinux.lds.S | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/tile/kernel/vmlinux.lds.S b/arch/tile/kernel/vmlinux.lds.S
> index e1baf094fba4..dcd7445c31a2 100644
> --- a/arch/tile/kernel/vmlinux.lds.S
> +++ b/arch/tile/kernel/vmlinux.lds.S
> @@ -1,3 +1,6 @@
> +/* Handle ro_after_init data on our own. */
> +#define RO_AFTER_INIT_DATA
> +
>  #include <asm-generic/vmlinux.lds.h>
>  #include <asm/page.h>
>  #include <asm/cache.h>
> @@ -87,6 +90,7 @@ SECTIONS
> 
>    _sdata = .;                   /* Start of data section */
>    RO_DATA_SECTION(PAGE_SIZE)
> +  RO_AFTER_INIT_DATA
>    RW_DATA_SECTION(L2_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
>    _edata = .;

imho, the minimal fix would be to just

#define __ro_after_init __read_mostly

within arch/tile/include/asm/cache.h. That's also what parisc currently
has.