On Mon, Jun 30, 2008 at 03:04:33PM -0700, H. Peter Anvin wrote:
quoted text
> Jeremy Fitzhardinge wrote:
> >It's a bit odd that the boot loader neglected to set up ds properly, but 
> >changing the testb line to
> >
> >    testb $(1<<6), %cs:BP_loadflags(%esi)
> >
> >should work.  (Or perhaps a %ss: override would be better?)
> >
> >I'm assuming that the GDT setup isn't completely mad and that the 
> >segments have the same base at least.
> >
> 
> This should have been set up by the *boot code* (specifically lines 
> 57-61 of arch/x86/boot/pmjump.S) since he's using a conventional boot 
> loader (syslinux) so something is utterly fuggled up.  Using %cs: here 
> should be safe, though (and *is* more conservative, after all, why 
> otherwise bother reloading these segments at all?), but it still 
> concerns me a great deal if this is broken in this way.  It's definitely 
> better than %ss:.
> 
> In particular, I'm wondering if the Elan CPU has any strange ordering 
> requirements with regards to the protected mode transition that we're 
> not obeying.
> 
> It would be interesting to put in a heavyweight "brutally synchronizing" 
> instruction like WBINVD at various places in arch/x86/boot/pmjump.S and 
> see if it helps.

You are right. With wbinvd before %ds is changed in that file the kernel
boots. 


Sean
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