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

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Date:	Fri, 09 Aug 2013 13:52:14 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, dave@...1.net,
	isimatu.yasuaki@...fujitsu.com,
	vasilis.liaskovitis@...fitbricks.com
Subject: Re: [PATCH] mm/hotplug: Verify hotplug memory range

On 08/09/2013 12:47 AM, Toshi Kani 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.
>
> Signed-off-by: Toshi Kani<toshi.kani@...com>
> ---
>   mm/memory_hotplug.c |   22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ca1dd3a..ac182de 100644
> --- 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("Unsupported hotplug range: start 0x%llx, size 0x%llx\n",
> +				start, size);

I think the message here should tell users that only support range aligned
to section. Others seems OK to me.

Reviewed-by: Tang Chen <tangchen@...fujitsu.com>

Thanks.

> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>   /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
>   int __ref add_memory(int nid, u64 start, u64 size)
>   {
> @@ -1078,6 +1094,10 @@ int __ref add_memory(int nid, u64 start, u64 size)
>   	struct resource *res;
>   	int ret;
>
> +	ret = check_hotplug_memory_range(start, size);
> +	if (ret)
> +		return ret;
> +
>   	lock_memory_hotplug();
>
>   	res = register_memory_resource(start, size);
> @@ -1786,6 +1806,8 @@ void __ref remove_memory(int nid, u64 start, u64 size)
>   {
>   	int ret;
>
> +	BUG_ON(check_hotplug_memory_range(start, size));
> +
>   	lock_memory_hotplug();
>
>   	/*
>
--
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