Messages in this thread | | | Date | Fri, 26 Aug 2011 22:09:30 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH 1/2] x86, ioapic: Reserve only 128 bytes for IOAPICs |
| |
On Fri, Aug 26, 2011 at 10:21:02AM -0600, Bjorn Helgaas wrote: ... > > > > Which means, I would prefer if we have (since we change IO_APIC_SLOT_SIZE > > anyway) some additional check and WARN_ON in this code. Something like > > > > if (io-apic-base-address & 0x3ff) > > WARN_ON(); > > > > Hm? (also we have bad_ioapic() check, probably should put such test > > there instead). > > Is there some spec that requires all IOAPICs to be 1K aligned? I > don't doubt that's the case; I'd just like to see something more > concrete than folklore. I'm pretty sure there's some (possibly > secret) "IOAPIC architecture spec," and a section reference to it > would be nice. Even before my patch, I don't think we actually > checked or enforced any *alignment* -- we only set the size. I don't > know if it's worth it unless we have a problem it would fix, and it's > conceivable that we'd start warning about a perfectly functional > IOAPIC that's 128-byte aligned. > > Bjorn
Yes, one of the spec is Intel's MP specification (as far as I remember). Letme re-check...
| 3.6.5 APIC Memory Mapping | | "Unlike the local APICs, the I/O APICs are mapped to give shared access from all | processors, providing full symmetric I/O access. The default base address for the | first I/O APIC is 0FEC0_0000h. Subsequent I/O APIC addresses are assigned in | 4K increments. For example, the second I/O APIC is at 0FEC0_1000h. Non-default | APIC base addresses can be used if the MP configuration table is provided. | (Refer to Chapter 4.) However, the local APIC base address must be aligned | on a 4K boundary, and the I/O APIC base address must be aligned on a 1K | boundary."
Ie -- 4K increment with 1K base address. If I find other sources I have in mind I'll ping you.
Cyrill -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |