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

Nate Lawson nate at
Wed Sep 22 10:57:47 PDT 2004

Bruce M Simpson wrote:
> 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.

Thanks, I work with SMIs a lot.  :)  The DDJ article is a good intro:


More information about the freebsd-current mailing list