efi_loader: Always allocate the highest available address

Some EFI applications (grub2) expect that an allocation always returns
the highest available memory address for the given size.

Without this, we may run into situations where the initrd gets allocated
at a lower address than the kernel.

This patch fixes booting in such situations for me.
Signed-off-by: NAlexander Graf <agraf@suse.de>

lib/efi_loader/efi_memory.c

@@ -13,6 +13,7 @@
 #include <malloc.h>
 #include <asm/global_data.h>
 #include <libfdt_env.h>
+#include <linux/list_sort.h>
 #include <inttypes.h>
 #include <watchdog.h>
 
@@ -26,6 +27,31 @@ struct efi_mem_list {
 /* This list contains all memory map items */
 LIST_HEAD(efi_mem);
 
+/*
+ * Sorts the memory list from highest address to lowest address
+ *
+ * When allocating memory we should always start from the highest
+ * address chunk, so sort the memory list such that the first list
+ * iterator gets the highest address and goes lower from there.
+ */
+static int efi_mem_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct efi_mem_list *mema = list_entry(a, struct efi_mem_list, link);
+	struct efi_mem_list *memb = list_entry(b, struct efi_mem_list, link);
+
+	if (mema->desc.physical_start == memb->desc.physical_start)
+		return 0;
+	else if (mema->desc.physical_start < memb->desc.physical_start)
+		return 1;
+	else
+		return -1;
+}
+
+static void efi_mem_sort(void)
+{
+	list_sort(NULL, &efi_mem, efi_mem_cmp);
+}
+
 /*
  * Unmaps all memory occupied by the carve_desc region from the
  * list entry pointed to by map.
@@ -142,6 +168,9 @@ uint64_t efi_add_memory_map(uint64_t start, uint64_t pages, int memory_type,
 	/* Add our new map */
         list_add_tail(&newlist->link, &efi_mem);
 
+	/* And make sure memory is listed in descending order */
+	efi_mem_sort();
+
 	return start;
 }