efi_loader: Merge memory map entries

We currently do not combine memory entries that are adjacent and have
the same attributes. The problem with that is that our memory map can
easily grow multiple hundreds of entries in a simple UEFI Shell
environment.

So let's make sure we always combine all entries to make the memory
map as small as possible. That way every other piece of code that
loops through it should also gain some nice speed ups.

Signed-off-by: Alexander Graf <agraf@suse.de>

lib/efi_loader/efi_memory.c

@@ -65,9 +65,54 @@ static int efi_mem_cmp(void *priv, struct list_head *a, struct list_head *b)
 		return -1;
 }
 
+static uint64_t desc_get_end(struct efi_mem_desc *desc)
+{
+	return desc->physical_start + (desc->num_pages << EFI_PAGE_SHIFT);
+}
+
 static void efi_mem_sort(void)
 {
+	struct list_head *lhandle;
+	struct efi_mem_list *prevmem = NULL;
+	bool merge_again = true;
+
 	list_sort(NULL, &efi_mem, efi_mem_cmp);
+
+	/* Now merge entries that can be merged */
+	while (merge_again) {
+		merge_again = false;
+		list_for_each(lhandle, &efi_mem) {
+			struct efi_mem_list *lmem;
+			struct efi_mem_desc *prev = &prevmem->desc;
+			struct efi_mem_desc *cur;
+			uint64_t pages;
+
+			lmem = list_entry(lhandle, struct efi_mem_list, link);
+			if (!prevmem) {
+				prevmem = lmem;
+				continue;
+			}
+
+			cur = &lmem->desc;
+
+			if ((desc_get_end(cur) == prev->physical_start) &&
+			    (prev->type == cur->type) &&
+			    (prev->attribute == cur->attribute)) {
+				/* There is an existing map before, reuse it */
+				pages = cur->num_pages;
+				prev->num_pages += pages;
+				prev->physical_start -= pages << EFI_PAGE_SHIFT;
+				prev->virtual_start -= pages << EFI_PAGE_SHIFT;
+				list_del(&lmem->link);
+				free(lmem);
+
+				merge_again = true;
+				break;
+			}
+
+			prevmem = lmem;
+		}
+	}
 }
 
 /** efi_mem_carve_out - unmap memory region