See arch/i386/kernel/smp.c around line 546 there is the code
If mpf->mpf_physptr is not set or if smp_read_mpc() finds no io_apic
then the default mapping for io_apic is not made (unlike previous
versions of the kernel). This panics on my (very old) SMP machine.
A simple fix is to follow the above code with
* We have an IO_APIC so use default if BIOS doesn't
* know about any
if (mp_apic_entries == 0)
mp_apics.mpc_apicaddr = mp_ioapic_addr;
Some additional fixes are also required for this machine (NCR 3416)
which contains a local external 82489DX apic. This doesn't seem to
want to work in logical mode, so I've also incorporated the fixes
proposed by James.Bottomley@columbiasc.ncr.com. It was by trying to
integrate his fix that I found this bug.
Created attachment 5 [details]
patch for NCR 3416 and rh 6.1
Assigned to dledford
Just as an Ingo FYI
whether such old systems (which usually do not conform to the Intel
Multiprocessor Specification) work with current kernels or not is a question of
luck. Logical delivery mode is pretty much a must for things like targetted IPI
delivery in the 2.4 kernel. Any patch that fixes such old systems should go
through "Maciej W. Rozycki" <email@example.com>, he is the author of most of
the external 82489DX APIC code.