+
+/**
+ * offline_memory_block_cb - callback function for offlining memory block
+ * @mem: the memory block to be offlined
+ * @arg: buffer to hold error msg
+ *
+ * Always return 0, and put the error msg in arg if any.
+ */
+static int offline_memory_block_cb(struct memory_block *mem, void *arg)
+{
+ int *ret = arg;
+ int error = offline_memory_block(mem);
+
+ if (error != 0 && *ret == 0)
+ *ret = error;
+
+ return 0;
+}
+
+static int is_memblock_offlined_cb(struct memory_block *mem, void *arg)
+{
+ int ret = !is_memblock_offlined(mem);
+
+ if (unlikely(ret))
+ pr_warn("removing memory fails, because memory "
+ "[%#010llx-%#010llx] is onlined\n",
+ PFN_PHYS(section_nr_to_pfn(mem->start_section_nr)),
+ PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1))-1);
+
+ return ret;
+}
+
+int __ref remove_memory(u64 start, u64 size)
+{
+ unsigned long start_pfn, end_pfn;
+ int ret = 0;
+ int retry = 1;
+
+ start_pfn = PFN_DOWN(start);
+ end_pfn = start_pfn + PFN_DOWN(size);
+
+ /*
+ * When CONFIG_MEMCG is on, one memory block may be used by other
+ * blocks to store page cgroup when onlining pages. But we don't know
+ * in what order pages are onlined. So we iterate twice to offline
+ * memory:
+ * 1st iterate: offline every non primary memory block.
+ * 2nd iterate: offline primary (i.e. first added) memory block.
+ */
+repeat:
+ walk_memory_range(start_pfn, end_pfn, &ret,
+ offline_memory_block_cb);
+ if (ret) {
+ if (!retry)
+ return ret;
+
+ retry = 0;
+ ret = 0;
+ goto repeat;
+ }
+
+ lock_memory_hotplug();
+
+ /*
+ * we have offlined all memory blocks like this:
+ * 1. lock memory hotplug
+ * 2. offline a memory block
+ * 3. unlock memory hotplug
+ *
+ * repeat step1-3 to offline the memory block. All memory blocks
+ * must be offlined before removing memory. But we don't hold the
+ * lock in the whole operation. So we should check whether all
+ * memory blocks are offlined.
+ */
+
+ ret = walk_memory_range(start_pfn, end_pfn, NULL,
+ is_memblock_offlined_cb);
+ if (ret) {
+ unlock_memory_hotplug();
+ return ret;
+ }
+
+ /* remove memmap entry */
+ firmware_map_remove(start, start + size, "System RAM");
+
+ arch_remove_memory(start, size);
+
+ unlock_memory_hotplug();
+
+ return 0;
+}