Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg_id

Ingo Molnar
2009-08-25T18:16:04Z

* Ravikiran G Thirumalai <kiran@scalex86.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@scalex86.org>
> >>>> Cc: Yinghai Lu <yinghai@kernel.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