Messages in this thread | ![/](/images/icornerl.gif) | | From | Bjorn Helgaas <> | Date | Fri, 26 Aug 2011 10:21:02 -0600 | Subject | Re: [PATCH 1/2] x86, ioapic: Reserve only 128 bytes for IOAPICs |
| |
On Fri, Aug 26, 2011 at 12:22 AM, Cyrill Gorcunov <gorcunov@gmail.com> wrote: > On Thu, Aug 25, 2011 at 06:17:06PM -0600, Bjorn Helgaas wrote: >> On Thu, Aug 25, 2011 at 5:33 PM, Suresh Siddha >> <suresh.b.siddha@intel.com> wrote: >> > On Thu, 2011-08-25 at 16:05 -0700, Bjorn Helgaas wrote: >> >> Previously we reserved 1024 bytes, but that's more space than the IOAPIC >> >> consumes, and it can cause conflicts with nearby devices. The known >> >> requirement is 68 bytes (sizeof(struct io_apic)), and rounding up to a >> >> power-of-2 gives us 128. >> >> >> > >> > Bjorn, Given the info from Intel that most of its io-apic >> > implementations has registers up to 0xff offset (reserved), does >> > reserving just the 128 bytes for the io-apic cause any address conflicts >> > if the next 128 bytes are allocated (by the OS) for any other device. >> >> If the OS allocated the next 128 bytes to another device, it sounds >> like it would cause a conflict on Intel boxes. This must be an area >> that differs between vendors. I haven't seen a spec that mentions 256 >> bytes as the required minimum MMIO size for IOAPICs, and apparently >> the AMD IOAPIC decodes 240 bytes or fewer. >> > > Hi Bjorn, > > the former idea (as far as I remember) of all this IO_APIC_SLOT_SIZE > was to be sure the io-apics are allocated with 1K step (which > is requirements for io-apics), but definitely it doesn't consume > that much space neither it decode the whole range. > > 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 -- 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/
| ![\](/images/icornerr.gif) |