ACK: [Xenial PATCH] arm64: mm: avoid calling apply_to_page_range on empty range

[Chris J Arges]

Acked-by: Chris J Arges <chris.j.arges at canonical.com>

On Mon, Feb 22, 2016 at 06:20:13PM +0800, Ming Lei wrote:
> From: Mika Penttilä <mika.penttila at nextfour.com>
> 
> Calling apply_to_page_range with an empty range results in a BUG_ON
> from the core code. This can be triggered by trying to load the st_drv
> module with CONFIG_DEBUG_SET_MODULE_RONX enabled:
> 
>   kernel BUG at mm/memory.c:1874!
>   Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>   Modules linked in:
>   CPU: 3 PID: 1764 Comm: insmod Not tainted 4.5.0-rc1+ #2
>   Hardware name: ARM Juno development board (r0) (DT)
>   task: ffffffc9763b8000 ti: ffffffc975af8000 task.ti: ffffffc975af8000
>   PC is at apply_to_page_range+0x2cc/0x2d0
>   LR is at change_memory_common+0x80/0x108
> 
> This patch fixes the issue by making change_memory_common (called by the
> set_memory_* functions) a NOP when numpages == 0, therefore avoiding the
> erroneous call to apply_to_page_range and bringing us into line with x86
> and s390.
> 
> BugLink: http://bugs.launchpad.net/bugs/1547718
> Cc: <stable at vger.kernel.org>
> Reviewed-by: Laura Abbott <labbott at redhat.com>
> Acked-by: David Rientjes <rientjes at google.com>
> Signed-off-by: Mika Penttilä <mika.penttila at nextfour.com>
> Signed-off-by: Will Deacon <will.deacon at arm.com>
> (cherry picked from commit 57adec866c0440976c96a4b8f5b59fb411b1cacb)
> Signed-off-by: Ming Lei <ming.lei at canonical.com>
> ---
>  arch/arm64/mm/pageattr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 3571c73..cf62407 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -57,6 +57,9 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	if (end < MODULES_VADDR || end >= MODULES_END)
>  		return -EINVAL;
>  
> +	if (!numpages)
> +		return 0;
> +
>  	data.set_mask = set_mask;
>  	data.clear_mask = clear_mask;
>  
> -- 
> 1.9.1
> 
> 
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