Re: [Xen-devel] [PATCH] xen-unstable on HP dc7800 simply reboots

[John Byrne <john.l.byrne@xxxxxx>]

John Byrne wrote:
> Keir Fraser wrote:
> > On 24/10/07 08:12, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> wrote:
> >
> > > > Littering the early boot code with putc() and comparing the code's
> > > > behavior on a machine that actually boots, I've found that the call to
> > > > get_memory_map from trampoline.S is the root of all evil. If that is
> > > > called, then the trampoline fails to make it back to protected mode 
> > > > from
> > > > real mode. I am still working to identify the specific problem.
> > > So if you remove that call, so Xen falls back to using the GRUB-supplied
> > > memory map, then Xen boots okay? Is tghat tru on current tip of 
> > > xen-unstable
> > > too?
> > Thinking some more my guess is that any BIOS call is causing you to 
> > crash,
> > so removing just teh call to get_memory_map will be insufficient on 
> > tip --
> > you'll have to remove calls to set video mode and get edd information 
> > too.
> > Perhaps the IDT is either corrupted or not actually at address 0x0, like
> > it's supposed to be? What happens if you remove the 'lidt' instruction 
> > from
> > arch/x86/boot/trampoline.S?
> Once I identified the problem revision, I went back to the tip to try to 
> debug it. (Sorry for any ambiguity.) Taking out get_memory_map is 
> sufficient;  get_edd and video don't seem to cause any problems. 
> Removing the lidt changes nothing. Adding a "ret" after the .Lmem88 in 
> mem.S confirms that the problem is in the e820 call. I'm currently 
> trying to see if the descriptor table is getting corrupted during the 
> BIOS calls.
A lot of work to find a one-line fix. There is no sign of any corruption 
in the GDT, but you do need to reload the GDT before transitioning back 
to real mode. I am asking a BIOS person might require this, but, in the 
meantime, I cannot see how this patch will cause trouble on any other 
system and it seems to fix mine. I am just a little uncomfortable 
because I don't really understand why it is required.
Signed-off-by: john.l.byrne@xxxxxx

Attachment: dc7800.patch
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