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    SubjectRe: [BUG] 2.5.63: ESR killed my box!

    On Wed, 26 Feb 2003, Ion Badulescu wrote:
    > Mikael's patch (included in the previous message) changes this to
    > boot_cpu_physical_apicid = -1U;
    > which is the same thing indeed.

    Yeah, I'd rather remove it if this is it.

    > It's not enough. There are two other problems, further down in
    > APIC_init_uniprocessor():
    > 1) apic_write_around(APIC_ID, boot_cpu_physical_apicid) places the APIC
    > value in the lower 8 bits of APIC_ID, when it should be in the upper 8. As
    > as result, it effectively forces the APIC id to always be 0 for the boot
    > CPU, which is fatal on SMP AMD boxes.

    Wouldn't it be nicer to just fix the write instead? I can see the
    potential to actually want to change the APIC ID - in particular, if the
    SMP MP tables say that the APIC ID for the BP should be X, maybe we should
    actually write X to it instead of just using what is there.

    In particular, Mikaels patch will BUG() if the MP tables don't match the
    APIC ID. I think that's extremely rude: we should select one of the two
    and just run with it, instead of unconditionally failing.

    > 2) phys_cpu_present_map = 1 means we always set bit 0, but later on
    > in setup_local_APIC() we do
    > if (!clustered_apic_mode &&
    > !test_bit(GET_APIC_ID(apic_read(APIC_ID)), &phys_cpu_present_map))
    > BUG();
    > and the bug is triggered if the APIC_ID is not zero.

    Yeah, there's no question something is wrong. However:

    > Here's Mikael's patch again -- it's quite obviously correct, it fixes the
    > problem on my SMP AMD boxes and doesn't break anything else I've thrown at
    > it. Applies cleanly to both 2.4 and 2.5.latest.

    I disagree with the "obviously correct", due to the above issue of
    mismatches between MP tables and actual APIC contents. I think it is more
    correct than what we have now, but..


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