linux-kernel - Re: x2apic boot failure on recent sandy bridge system

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Date:	Mon, 12 Dec 2011 16:25:02 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"Berck E. Nash" <flyboy@...il.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: x2apic boot failure on recent sandy bridge system

On Mon, 2011-12-12 at 15:21 -0800, Berck E. Nash wrote:
> On 12/11/2011 08:40 PM, Yinghai Lu wrote:
> > x2apic pre-enabled skip the mapping for lapic address. so need map it
> > after fall back.
> > 
> > please check attached -v5..
> 
> It appears to work correctly as far as I can tell.

Ok. In this case, it looks like bios didn't enable interrupt-remapping
(part of vt-d) and just enabled x2apic with out touching or exporting
vt-d HW.

Yinghai, In other scenarios where OS can't recover, mostly likely we
will fail in check_timer() when we fall back to xapic. Can we add a
printk in this case to convey the potential reason (that I mentioned in
the previous e-mail), so that the user can get more accurate information
for the check timer failure.

thanks,
suresh

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