Re: x2apic boot failure on recent sandy bridge system

From: Suresh Siddha
Date: Fri Oct 19 2012 - 19:02:01 EST

On Fri, 2012-10-19 at 13:42 -0700, rrl125@xxxxxxxxx wrote:
> Any update? The messages just seem to have stopped months ago. A
> fallback would be nice, I have been booting the kernel with noa2xpic
> for since kernel 3.2, and currently I am working with 3.6.2.
> If needed I can try to attempt modifying the patch to include
> fallback, but I am probably not the best person to do it.

Are you referring to this commit that made into the mainline tree

commit fb209bd891645bb87b9618b724f0b4928e0df3de
Author: Yinghai Lu <yinghai@xxxxxxxxxx>
Date: Wed Dec 21 17:45:17 2011 -0800

x86, x2apic: Fallback to xapic when BIOS doesn't setup interrupt-remapping

On some of the recent Intel SNB platforms, by default bios is pre-enabling
x2apic mode in the cpu with out setting up interrupt-remapping.
This case was resulting in the kernel to panic as the cpu is already in
x2apic mode but the OS was not able to enable interrupt-remapping (which
is a pre-req for using x2apic capability).

On these platforms all the apic-ids are < 255 and the kernel can fallback to
xapic mode if the bios has not enabled interrupt-remapping (which is
mostly the case if the bios has not exported interrupt-remapping tables to the

Reported-by: Berck E. Nash <flyboy@xxxxxxxxx>
Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>

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