- /* Initialise the balloon with excess memory space. */
- extra_pfn_end = min(e820_end_of_ram_pfn(),
+ /*
+ * Initialise the balloon with excess memory space. We need
+ * to make sure we don't add memory which doesn't exist or
+ * logically exist. The E820 map can be trimmed to be smaller
+ * than the amount of physical memory due to the mem= command
+ * line parameter. And if this is a 32-bit non-HIGHMEM kernel
+ * on a system with memory which requires highmem to access,
+ * don't try to use it.
+ */
+ extra_pfn_end = min(min(max_pfn, e820_end_of_ram_pfn()),