On my system, 2.4.19pre3 hangs to hard reset just after it prints
"Intel machine check architecture supported."  If I pass "nomce" on the
command line, it boots fine. 2.2.20 did not have a problem enabling
machine checks.  I instrumented 2.4's bluesmoke.c and determined that
it hangs trying to clear the second of five IA32_MC0_CTL banks
(i.e. the second iteration of the loop

        for(i=0;i<banks;i++)
        {
                wrmsr(MSR_IA32_MC0_CTL+4*i, 0xffffffff, 0xffffffff);
        }

in intel_mcheck_init())

This is an older P-III CPU (stepping 3, 500MHz) and a 440BX/ZX chipset.
Compiler used was 2.95.4.  dmesg (from a nomce boot), lspci -v, and
.config are attached to the message.  Please let me know if you need
more information.

I'm not subscribed to linux-kernel, please cc: me directly on replies.

zw