linux-kernel - Re: [PATCH v2] mm/hotplug: Verify hotplug memory range

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Date:	Wed, 14 Aug 2013 15:09:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...fujitsu.com, kamezawa.hiroyu@...fujitsu.com,
	dave@...1.net, isimatu.yasuaki@...fujitsu.com,
	tangchen@...fujitsu.com, vasilis.liaskovitis@...fitbricks.com
Subject: Re: [PATCH v2] mm/hotplug: Verify hotplug memory range

On Sat, 10 Aug 2013 13:17:32 -0600 Toshi Kani <toshi.kani@...com> wrote:

> add_memory() and remove_memory() can only handle a memory range aligned
> with section.  There are problems when an unaligned range is added and
> then deleted as follows:
> 
>  - add_memory() with an unaligned range succeeds, but __add_pages()
>    called from add_memory() adds a whole section of pages even though
>    a given memory range is less than the section size.
>  - remove_memory() to the added unaligned range hits BUG_ON() in
>    __remove_pages().
> 
> This patch changes add_memory() and remove_memory() to check if a given
> memory range is aligned with section at the beginning.  As the result,
> add_memory() fails with -EINVAL when a given range is unaligned, and
> does not add such memory range.  This prevents remove_memory() to be
> called with an unaligned range as well.  Note that remove_memory() has
> to use BUG_ON() since this function cannot fail.
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1069,6 +1069,22 @@ out:
>  	return ret;
>  }
>  
> +static int check_hotplug_memory_range(u64 start, u64 size)
> +{
> +	u64 start_pfn = start >> PAGE_SHIFT;
> +	u64 nr_pages = size >> PAGE_SHIFT;
> +
> +	/* Memory range must be aligned with section */
> +	if ((start_pfn & ~PAGE_SECTION_MASK) ||
> +	    (nr_pages % PAGES_PER_SECTION) || (!nr_pages)) {
> +		pr_err("Section-unaligned hotplug range: start 0x%llx, size 0x%llx\n",
> +				start, size);

Printing a u64 is problematic.  Here you assume that u64 is implemented
as unsigned long long.  But it can be implemented as unsigned long, by
architectures which use include/asm-generic/int-l64.h.  Such an
architecture will generate a compile warning here, but I can't
immediately find a Kconfig combination which will make that happen.

> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}

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