xtensa: fix high memory/reserved memory collision

commit 6ac5a11 upstream.

Xtensa memory initialization code frees high memory pages without
checking whether they are in the reserved memory regions or not. That
results in invalid value of totalram_pages and duplicate page usage by
CMA and highmem. It produces a bunch of BUGs at startup looking like
this:

BUG: Bad page state in process swapper  pfn:70800
page:be60c000 count:0 mapcount:-127 mapping:  (null) index:0x1
flags: 0x80000000()
raw: 80000000 00000000 00000001 ffffff80 00000000 be60c014 be60c014 0000000a
page dumped because: nonzero mapcount
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Tainted: G    B            4.16.0-rc1-00015-g7928b2cbe55b-dirty #23
Stack:
 bd839d33 00000000 00000018 ba97b64c a106578c bd839d70 be60c000 00000000
 a1378054 bd86a000 00000003 ba97b64c a1066166 bd839da0 be60c000 ffe00000
 a1066b58 bd839dc0 be504000 00000000 000002f4 bd838000 00000000 0000001e
Call Trace:
 [<a1065734>] bad_page+0xac/0xd0
 [<a106578c>] free_pages_check_bad+0x34/0x4c
 [<a1066166>] __free_pages_ok+0xae/0x14c
 [<a1066b58>] __free_pages+0x30/0x64
 [<a1365de5>] init_cma_reserved_pageblock+0x35/0x44
 [<a13682dc>] cma_init_reserved_areas+0xf4/0x148
 [<a10034b8>] do_one_initcall+0x80/0xf8
 [<a1361c16>] kernel_init_freeable+0xda/0x13c
 [<a125b59d>] kernel_init+0x9/0xd0
 [<a1004304>] ret_from_kernel_thread+0xc/0x18

Only free high memory pages that are not reserved.

Cc: stable@vger.kernel.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/xtensa/mm/init.c

@@ -79,19 +79,75 @@ void __init zones_init(void)
 	free_area_init_node(0, zones_size, ARCH_PFN_OFFSET, NULL);
 }
 
+#ifdef CONFIG_HIGHMEM
+static void __init free_area_high(unsigned long pfn, unsigned long end)
+{
+	for (; pfn < end; pfn++)
+		free_highmem_page(pfn_to_page(pfn));
+}
+
+static void __init free_highpages(void)
+{
+	unsigned long max_low = max_low_pfn;
+	struct memblock_region *mem, *res;
+
+	reset_all_zones_managed_pages();
+	/* set highmem page free */
+	for_each_memblock(memory, mem) {
+		unsigned long start = memblock_region_memory_base_pfn(mem);
+		unsigned long end = memblock_region_memory_end_pfn(mem);
+
+		/* Ignore complete lowmem entries */
+		if (end <= max_low)
+			continue;
+
+		if (memblock_is_nomap(mem))
+			continue;
+
+		/* Truncate partial highmem entries */
+		if (start < max_low)
+			start = max_low;
+
+		/* Find and exclude any reserved regions */
+		for_each_memblock(reserved, res) {
+			unsigned long res_start, res_end;
+
+			res_start = memblock_region_reserved_base_pfn(res);
+			res_end = memblock_region_reserved_end_pfn(res);
+
+			if (res_end < start)
+				continue;
+			if (res_start < start)
+				res_start = start;
+			if (res_start > end)
+				res_start = end;
+			if (res_end > end)
+				res_end = end;
+			if (res_start != start)
+				free_area_high(start, res_start);
+			start = res_end;
+			if (start == end)
+				break;
+		}
+
+		/* And now free anything which remains */
+		if (start < end)
+			free_area_high(start, end);
+	}
+}
+#else
+static void __init free_highpages(void)
+{
+}
+#endif
+
 /*
  * Initialize memory pages.
  */
 
 void __init mem_init(void)
 {
-#ifdef CONFIG_HIGHMEM
-	unsigned long tmp;
-
-	reset_all_zones_managed_pages();
-	for (tmp = max_low_pfn; tmp < max_pfn; tmp++)
-		free_highmem_page(pfn_to_page(tmp));
-#endif
+	free_highpages();
 
 	max_mapnr = max_pfn - ARCH_PFN_OFFSET;
 	high_memory = (void *)__va(max_low_pfn << PAGE_SHIFT);