Re: [Fedora-ia64-list] kernel 2.6.16-1.2097_FC6 unbootable on Itanium

From: Jack Steiner <steiner_at_sgi.com>
Date: 2006-03-31 02:49:07
On Thu, Mar 30, 2006 at 08:43:43AM -0700, David Mosberger-Tang wrote:
> On 3/30/06, Jack Steiner <steiner@sgi.com> wrote:
> 
> > Is this problem unique to SN systems
> 
> No, the same will happen on all other systems (that I know of).
> 
> > The BIOS reports that most
> > memory ranges support both CACHED & UNCACHED references. I _think_
> > this is correct.
> 
> That's correct.  The map shows the ways the page *can* be mapped, not
> the way it *should* be mapped.
> 
> It's strange that ACPI would prefer to use WC when WB mapping is
> possible.  They definitely need to pick one way and stick with it
> though.  As you say, mapping the same page with different cacheability
> is a no-no (and at least in theory, it should cause an MCA even on
> real hardware).

It does, at least on our chipset. If the chipset detects a simultaneous
UC & C reference, it generates a BUS error. It is surprising how
quickly this MCA occurs when we break the rules.



> 
>   --david
> 
> --
> Mosberger Consulting LLC, http://www.mosberger-consulting.com/

-- 
Jack


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Received on Fri Mar 31 02:50:31 2006

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