xen/e820: Guard against E820_RAM not having page-aligned size or start.

Under Dell Inspiron 1525, and Intel SandyBridge SDP's the
BIOS e820 RAM is not page-aligned:

[   0.000000]  Xen: 0000000000100000 - 00000000df66d800 (usable)

We were not handling that and ended up setting up a pagetable
that included up to df66e000 with the disastrous effect that when

        memset(NODE_DATA(nodeid), 0, sizeof(pg_data_t));

tried to clear the page it would crash at the 2K mark.

Initially reported by Michael Young @
http://lists.xensource.com/archives/html/xen-devel/2011-01/msg00108.html

The fix is to page-align the size and also take into consideration
the start of the E820 (in case that is not page-aligned either). This
fixes the bootup failure on those affected machines.

This patch is a rework of the Micheal A Young initial patch and
considers the case if the start is not page-aligned.

Reported-by: Michael A Young <m.a.young@durham.ac.uk>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Michael A Young <m.a.young@durham.ac.uk>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index b5a7f928234b..75bdf2ab3d7c 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -179,8 +179,13 @@ char * __init xen_memory_setup(void)
         e820.nr_map = 0;
         xen_extra_mem_start = mem_end;
         for (i = 0; i < memmap.nr_entries; i++) {
-                unsigned long long end = map[i].addr + map[i].size;
+                unsigned long long end;
 
+                /* Guard against non-page aligned E820 entries. */
+                if (map[i].type == E820_RAM)
+                        map[i].size -= (map[i].size + map[i].addr) % PAGE_SIZE;
+
+                end = map[i].addr + map[i].size;
                 if (map[i].type == E820_RAM && end > mem_end) {
                         /* RAM off the end - may be partially included */
                         u64 delta = min(map[i].size, end - mem_end);