xen: don't add extra_pages for RAM after mem_end

If an E820 region is entirely beyond mem_end, don't attempt to truncate
it and add the truncated pages to extra_pages, as they will be negative.

Also, make sure the extra memory region starts after all BIOS provided
E820 regions (and in the case of RAM regions, post-clipping).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 14 insertions, 9 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index cad2fcd130ec..7a4ab05cff8a 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -52,20 +52,19 @@ phys_addr_t xen_extra_mem_start, xen_extra_mem_size;
 static __init void xen_add_extra_mem(unsigned long pages)
 {
         u64 size = (u64)pages * PAGE_SIZE;
+        u64 extra_start = xen_extra_mem_start + xen_extra_mem_size;
 
         if (!pages)
                 return;
 
-        e820_add_region(xen_extra_mem_start + xen_extra_mem_size, size, E820_RAM);
+        e820_add_region(extra_start, size, E820_RAM);
         sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
-        reserve_early(xen_extra_mem_start + xen_extra_mem_size,
-                      xen_extra_mem_start + xen_extra_mem_size + size,
-                      "XEN EXTRA");
+        reserve_early(extra_start, extra_start + size, "XEN EXTRA");
 
         xen_extra_mem_size += size;
 
-        xen_max_p2m_pfn = PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size);
+        xen_max_p2m_pfn = PFN_DOWN(extra_start + size);
 }
 
 static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
@@ -175,15 +174,21 @@ char * __init xen_memory_setup(void)
                 unsigned long long end = map[i].addr + map[i].size;
 
                 if (map[i].type == E820_RAM) {
-                        if (end > mem_end) {
+                        if (map[i].addr < mem_end && end > mem_end) {
                                 /* Truncate region to max_mem. */
-                                map[i].size -= end - mem_end;
+                                u64 delta = end - mem_end;
 
-                                extra_pages += PFN_DOWN(end - mem_end);
+                                map[i].size -= delta;
+                                extra_pages += PFN_DOWN(delta);
+
+                                end = mem_end;
                         }
-                } else if (map[i].type != E820_RAM)
+                }
+
+                if (end > xen_extra_mem_start)
                         xen_extra_mem_start = end;
 
+                /* If region is non-RAM or below mem_end, add what remains */
                 if ((map[i].type != E820_RAM || map[i].addr < mem_end) &&
                     map[i].size > 0)
                         e820_add_region(map[i].addr, map[i].size, map[i].type);