Messages in this thread | | | Date | Fri, 26 Aug 2011 10:22:24 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH 1/2] x86, ioapic: Reserve only 128 bytes for IOAPICs |
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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).
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/
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