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Re: [Qemu-devel] [ipxe-devel] Big real mode use in ipxe


From: Kevin O'Connor
Subject: Re: [Qemu-devel] [ipxe-devel] Big real mode use in ipxe
Date: Sun, 19 Aug 2012 11:53:32 -0400
User-agent: Mutt/1.5.21 (2010-09-15)

On Sun, Aug 19, 2012 at 04:34:50PM +0100, Michael Brown wrote:
> On Sunday 19 Aug 2012 16:07:05 Avi Kivity wrote:
> > (and that seabios needs changes to either work in
> > big real mode, or to put the processor back into big real mode after
> > returning from a PMM service.
> 
> If seabios switches into protected mode when performing a PMM service, then 
> it 
> _must_ leave the segment limits at 4G when returning to real mode.  To do 
> otherwise will violate the PMM spec, and will break conforming clients such 
> as 
> iPXE.

SeaBIOS does switch to 32bit mode during PMM calls and does switch to
16bit "big real" mode (segment limits set to 4G) on return.

-Kevin



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