x86: Exclude E820_RESERVED regions and memory holes above 4 GB from direct mapping.

On systems with very large memory (1 TB in our case), BIOS may report a
reserved region or a hole in the E820 map, even above the 4 GB range. Exclude
these from the direct mapping.

[ hpa: this should be done not just for > 4 GB but for everything above the legacy
  region (1 MB), at the very least.  That, however, turns out to require significant
  restructuring.  That work is well underway, but is not suitable for rc/stable. ]

Cc: stable@kernel.org   # > 2.6.32
Signed-off-by: Jacob Shin <jacob.shin@amd.com>
Link: http://lkml.kernel.org/r/1319145326-13902-1-git-send-email-jacob.shin@amd.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/kernel/setup.c

@@ -919,8 +919,21 @@ void __init setup_arch(char **cmdline_p)
 
 #ifdef CONFIG_X86_64
 	if (max_pfn > max_low_pfn) {
-		max_pfn_mapped = init_memory_mapping(1UL<<32,
-						     max_pfn<<PAGE_SHIFT);
+		int i;
+		for (i = 0; i < e820.nr_map; i++) {
+			struct e820entry *ei = &e820.map[i];
+
+			if (ei->addr + ei->size <= 1UL << 32)
+				continue;
+
+			if (ei->type == E820_RESERVED)
+				continue;
+
+			max_pfn_mapped = init_memory_mapping(
+				ei->addr < 1UL << 32 ? 1UL << 32 : ei->addr,
+				ei->addr + ei->size);
+		}
+
 		/* can we preseve max_low_pfn ?*/
 		max_low_pfn = max_pfn;
 	}