mp_machdep.c (was Re: [Fwd: Re: Bug reports requested - acpi])

Bruce M Simpson bms at
Wed Sep 22 02:04:33 PDT 2004

Just FYI...

On Tue, Sep 21, 2004 at 02:41:42PM -0400, John Baldwin wrote:
> Umm, 0xa0000 is the start of Video RAM, so I sure hope the ACPI wake code 
> doesn't try to write code into Video memory.  The pmap_invalidate_page is 
> certainly needed.

This is more common than you'd think, by the way. The 0xA0000 range is
sometimes used as a place to hold 'hidden memory' used whilst servicing
an SMI; ie the pages are 'stolen' from main memory by the during BIOS
initialization using registers for APM/ACPI support in the chipset.

Sometimes this is referred to as SMRAM or Systems Management Memory (SMM).
I posted some code just over a year ago illustrating how to access this
'hidden segment' on the i440BX to the lists.


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