Hi,

On Tue, 31 Jul 2001, Linus Torvalds wrote:
> In article <Pine.LNX.4.21.0107310705580.1374-100000@penguin.homenet> you write:
> >
> >Isn't SMP P6 kernel supposed to boot fine on a P4? Btw, booting with
> >"nosmp" works but booting with "noapic" hangs just the same.
>
> It should boot, and it looks like the problem may be a bad MP table.


  The problem is the MP table contains no configuration blocks, and a zero
local APIC address.  I've attached the full boot messages.

  The work around is trap that there are no config blocks, and fall back
to UP.  Patch attached.

Mark



diff -ur -X dontdiff linux-2.4.7/arch/i386/kernel/apic.c p4-2.4.7/arch/i386/kernel/apic.c
--- linux-2.4.7/arch/i386/kernel/apic.c	Wed Jun 20 18:06:38 2001
+++ p4-2.4.7/arch/i386/kernel/apic.c	Fri Aug  3 11:10:55 2001
@@ -345,9 +345,8 @@
 {
 	unsigned long apic_phys;

-	if (smp_found_config) {
-		apic_phys = mp_lapic_addr;
-	} else {
+	apic_phys = mp_lapic_addr;
+	if (!apic_phys) {
 		/*
 		 * set up a fake all zeroes page to simulate the
 		 * local APIC and another one for the IO-APIC. We
diff -ur -X dontdiff linux-2.4.7/arch/i386/kernel/mpparse.c p4-2.4.7/arch/i386/kernel/mpparse.c
--- linux-2.4.7/arch/i386/kernel/mpparse.c	Tue Jun 12 02:15:27 2001
+++ p4-2.4.7/arch/i386/kernel/mpparse.c	Fri Aug  3 11:04:18 2001
@@ -306,6 +306,23 @@
 	mp_lapic_addr = mpc->mpc_lapic;

 	/*
+	 * Buggy BIOS work around.
+	 * Some BIOSes report an MP table, with correct signature, checksum,
+	 * etc, but with no configuration blocks.
+	 * In this case fall back to UP.
+	 *
+	 * Note: On a system which showed this problem, the local APIC
+	 * address was given as NULL.  This may not be the case for all
+	 * systems, so take the address (incase it is valid) and check it
+	 * init_apic_mappings().
+	 */
+	if (count >= mpc->mpc_length) {
+		printk("Short mptable - assuming UP system\n");
+		smp_found_config = 0;
+		return 1;
+	}
+
+	/*
 	 *	Now process the configuration blocks.
 	 */
 	while (count < mpc->mpc_length) {