linux-kernel - Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg

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Date:	Tue, 25 Aug 2009 20:15:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
Cc:	Yinghai Lu <yinghai@...nel.org>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, shai@...lex86.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg_id


* Ravikiran G Thirumalai <kiran@...lex86.org> wrote:

> On Mon, Aug 24, 2009 at 10:12:01PM -0700, Yinghai Lu wrote:
> >Ravikiran G Thirumalai wrote:
> >> On Mon, Aug 24, 2009 at 04:53:45PM -0700, Yinghai Lu wrote:
> >>> Ravikiran G Thirumalai wrote:
> >>>> Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
> >>>> Cc: Yinghai Lu <yinghai@...nel.org>
> >>>>
> >>>
> >> 
> >> Why?  The specs seem to indicate otherwise unless I am mistaken --
> >> Intel  systems programming guide, Vol 3A Part1, chapter 7 section
> >> 7.5.5 - Identifying Logical Processors in a MP system:
> >> <quote>
> >> After the BIOS has completed the MP initialization protocol, each logical
> >> processor can be uniquely identified by its local APIC ID. Software can
> >> access these APIC IDs in either of the following ways
> >> </quote>
> >> phys_pkg_id() indicates that the logical package id is being looked up,
> >> so local apic id should be used here no?
> >> What am I missing?
> >
> >initial apic id : it can not changed, there is fixed mapping from that to physical processor id aka socket id / node id.
> >
> >apic id: could be changed by BIOS to any value. there is no good way to get phys_pkg_id from that.
> >
> 
> But BIOS is supposed to change it to a sane value.  Until 2.6.30, 
> local apic id has been used to get phys_pkg_id for the 'flat' 
> apics!  What changed?  Was this changed for a BIOS bug?  Even the 
> intel books seem to indicate local apic usage!

We should revert to the .30 behavior unless there's a good reason 
(even in that case we'll solve the regression and do a workaround 
for vSMP). Yinghai?

	Ingo
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