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Subject: Re: [PATCH] xen: unexport __init-annotated
 xen_xlate_map_ballooned_pages()
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        moderated for non-subscribers <xen-devel@lists.xenproject.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Julien Grall <julien.grall@arm.com>,
        Shannon Zhao <shannon.zhao@linaro.org>,
        linux-kernel@vger.kernel.org
References: <20220606045920.4161881-1-masahiroy@kernel.org>
From:   Oleksandr <olekstysh@gmail.com>
Message-ID: <20c9cd23-429f-896c-b59b-c518ff2562e2@gmail.com>
Date:   Mon, 6 Jun 2022 19:17:56 +0300
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On 06.06.22 07:59, Masahiro Yamada wrote:

Hello

> EXPORT_SYMBOL and __init is a bad combination because the .init.text
> section is freed up after the initialization. Hence, modules cannot
> use symbols annotated __init. The access to a freed symbol may end up
> with kernel panic.
>
> modpost used to detect it, but it has been broken for a decade.
>
> Recently, I fixed modpost so it started to warn it again, then this
> showed up in linux-next builds.
>
> There are two ways to fix it:
>
>    - Remove __init
>    - Remove EXPORT_SYMBOL
>
> I chose the latter for this case because none of the in-tree call-sites
> (arch/arm/xen/enlighten.c, arch/x86/xen/grant-table.c) is compiled as
> modular.

Good description.


>
> Fixes: 243848fc018c ("xen/grant-table: Move xlated_setup_gnttab_pages to common place")
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

I think the patch is correct.

Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

> ---
>
>   drivers/xen/xlate_mmu.c | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> index 34742c6e189e..f17c4c03db30 100644
> --- a/drivers/xen/xlate_mmu.c
> +++ b/drivers/xen/xlate_mmu.c
> @@ -261,7 +261,6 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt,
>   
>   	return 0;
>   }
> -EXPORT_SYMBOL_GPL(xen_xlate_map_ballooned_pages);
>   
>   struct remap_pfn {
>   	struct mm_struct *mm;

-- 
Regards,

Oleksandr Tyshchenko