diff -r 0016f5a1dd5a xen/arch/x86/cpu/amd.c
--- a/xen/arch/x86/cpu/amd.c	Thu May 15 15:11:29 2008 +0100
+++ b/xen/arch/x86/cpu/amd.c	Fri May 23 10:46:27 2008 +0200
@@ -86,9 +86,11 @@ static void disable_c1_ramping(void)
 static void disable_c1_ramping(void) 
 {
 	u8 pmm7;
-	int node;
-
-	for (node=0; node < NR_CPUS; node++) {
+	int node, nr_nodes;
+
+	/* read the number of nodes from the first northbridge */
+	nr_nodes = ((pci_read_byte(0, 0x18, 0x0, 0x60)>>4)&0x07)+1;
+	for (node=0; node < nr_nodes; node++) {
 		/* PMM7: bus=0, dev=0x18+node, function=0x3, register=0x87. */
 		pmm7 = pci_read_byte(0, 0x18+node, 0x3, 0x87);
 		/* Invalid read means we've updated every Northbridge. */