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SubjectRe: [PATCH v2] mm/hotplug: Verify hotplug memory range
On Sat, 10 Aug 2013 13:17:32 -0600 Toshi Kani <toshi.kani@hp.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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