Both v and vb->num_pages are u32 and unsigned int respectively. If v is less
than vb->num_pages (and it is, when deflating the balloon), the result is a
very large 32-bit number. Since we're returning a s64, instead of getting the
same negative number we desire, we get a very large positive number.
This handles the case where v < vb->num_pages and ensures we get a small,
negative, s64 as the result.
Rusty: please push this for 2.6.27-rc4. It's probably appropriate for the
stable tree too as it will cause an unexpected OOM when ballooning.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (simplified)
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