Re: Problems with EDAC coexisting with BIOS

[thockin]

On Wed, May 03, 2006 at 09:25:01PM +0100, Tim Small wrote:
> existing BIOSs, but the EDAC module could reprogram the chipset 
> error-signalling registers, so that an ECC error no longer triggers an 

This is key, I think.

> SMI.  The BIOS SMI handler could then read the signalling registers, and 
> leave the ECC registers well alone if ECC errors are not set to generate 
> an SMI.

The fundamental problem with SMI is that we CAN'T know what it is doing.
I've seen systems which trigger SMI from a GPIO toggled by a clock.  I've
seen systems trigger SMI from a chipset-internal periodic timer.  I've
seen chipsets route NMI->SMI or even MCE->SMI.  If the BIOS is polling the
error status registers from a periodic SMI, we're GOING to lose data.

The big hammer - turn off SMI - is probably OK on some systems, but is not
a general solution.  More and more hardware workarounds and features are
SMI based.  There are some rather interesting things that can be done in
SMM, *iff* we could get the BIOS out of the way.

Tim (watching EDAC from time to time, quietly)
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