x86, e820, pci: reserve extra free space near end of RAM

The point is to take all RAM resources we have, and
_after_ we've added all the resources we've seen in
the E820 tree, we then _also_ try to add fake reserved
entries for any "round up to X" at the end of the RAM
resources.

[ Impact: improve PCI mem-resource allocation robustness, protect "stolen RAM" ]

Reported-by: Yannick Roehlly <yannick.roehlly@free.fr>
Acked-by: Jesse Barnes <jesse.barnes@intel.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: yannick.roehlly@free.fr
LKML-Reference: <4A01A784.2050407@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/e820.c

@@ -1371,6 +1371,23 @@ void __init e820_reserve_resources(void)
 	}
 }
 
+/* How much should we pad RAM ending depending on where it is? */
+static unsigned long ram_alignment(resource_size_t pos)
+{
+	unsigned long mb = pos >> 20;
+
+	/* To 64kB in the first megabyte */
+	if (!mb)
+		return 64*1024;
+
+	/* To 1MB in the first 16MB */
+	if (mb < 16)
+		return 1024*1024;
+
+	/* To 32MB for anything above that */
+	return 32*1024*1024;
+}
+
 void __init e820_reserve_resources_late(void)
 {
 	int i;
@@ -1382,6 +1399,24 @@ void __init e820_reserve_resources_late(void)
 			insert_resource_expand_to_fit(&iomem_resource, res);
 		res++;
 	}
+
+	/*
+	 * Try to bump up RAM regions to reasonable boundaries to
+	 * avoid stolen RAM:
+	 */
+	for (i = 0; i < e820.nr_map; i++) {
+		struct e820entry *entry = &e820_saved.map[i];
+		resource_size_t start, end;
+
+		if (entry->type != E820_RAM)
+			continue;
+		start = entry->addr + entry->size;
+		end = round_up(start, ram_alignment(start));
+		if (start == end)
+			continue;
+		reserve_region_with_split(&iomem_resource, start,
+						  end - 1, "RAM buffer");
+	}
 }
 
 char *__init default_machine_specific_memory_setup(void)