[PATCH] mm/hotplug: Verify hotplug memory range

From: Toshi Kani
Date: Thu Aug 08 2013 - 12:49:18 EST

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

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@xxxxxx>
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);
+ 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;

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));

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