x86/uv: fix init of cpu-less nodes

Fix an endcase in the UV initialization code for the "UV large system mode"
of apicids.  If node zero contains no cpus, cpus on another node will be the
boot cpu.  The percpu data that contains the extra apicid bits was not
being initialized early enough.

[ Impact: fix potential boot crash on cpu-less UV nodes ]
Signed-off-by: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20090417142447.GA23759@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/apic/x2apic_uv_x.c

@@ -19,6 +19,7 @@
 #include <linux/timer.h>
 #include <linux/cpu.h>
 #include <linux/init.h>
+#include <linux/io.h>
 
 #include <asm/uv/uv_mmrs.h>
 #include <asm/uv/uv_hub.h>
@@ -34,6 +35,17 @@ DEFINE_PER_CPU(int, x2apic_extra_bits);
 
 static enum uv_system_type uv_system_type;
 
+static int early_get_nodeid(void)
+{
+	union uvh_node_id_u node_id;
+	unsigned long *mmr;
+
+	mmr = early_ioremap(UV_LOCAL_MMR_BASE | UVH_NODE_ID, sizeof(*mmr));
+	node_id.v = *mmr;
+	early_iounmap(mmr, sizeof(*mmr));
+	return node_id.s.node_id;
+}
+
 static int uv_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
 {
 	if (!strcmp(oem_id, "SGI")) {
@@ -42,6 +54,8 @@ static int uv_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
 		else if (!strcmp(oem_table_id, "UVX"))
 			uv_system_type = UV_X2APIC;
 		else if (!strcmp(oem_table_id, "UVH")) {
+			__get_cpu_var(x2apic_extra_bits) =
+				early_get_nodeid() << (UV_APIC_PNODE_SHIFT - 1);
 			uv_system_type = UV_NON_UNIQUE_APIC;
 			return 1;
 		}