[SeaBIOS] varlow/extrastack vs code

[Dr. David Alan Gilbert]

* Paolo Bonzini (pbonzini at redhat.com) wrote:
> 
> 
> On 18/02/2017 17:55, Kevin O'Connor wrote:
> > On Sat, Feb 18, 2017 at 04:11:28PM +0100, Paolo Bonzini wrote:
> >> On 18/02/2017 04:45, Kevin O'Connor wrote:
> >>> On Fri, Feb 17, 2017 at 02:12:57PM +0100, Paolo Bonzini wrote:
> >>>> On 15/02/2017 18:35, Dr. David Alan Gilbert wrote:
> >>>>> Yes it seems to.
> >>>>> One worry is that if we ever fix the qemu triple-fault so it really
> >>>>> does what you're describing and only resets the CPU, then I'm not
> >>>>> sure your int3 is the right choice.
> >>>>>
> >>>>> The other question is whether that protected-mode exit switch
> >>>>> works in practice on qemu; it's going to come back with a lot of it's
> >>>>> devices reset.
> >>>>
> >>>> Right, keyboard reset (and port 92h reset) should be an INIT and not a
> >>>> full system reset.  But that's also something that should be fixed, not
> >>>> a quirk to rely on...
> >>>
> >>> Could we rely on the pci reset mechanism (port 0xcf9)?
> >>
> >> That's only 3-4 years old, but 0xcf9 followed by keyboard reset should
> >> always work.
> > 
> > Since this would be qemu specific, I think it would be okay if reset
> > only worked on qemu versions from the last few years.  Or, are you
> > saying only some machine types would support it?  I checked, and
> > reboots on isapc don't currently work at all (looks like the bios
> > isn't mapped to 0xfff00000 on isapc) so I don't think that's a
> > stopper.
> 
> isapc should never be SMP, so the keyboard reset would be enough even if
> it were fixed to be an INIT.  Hence my suggestion of using 0xcf9 for
> recent QEMU with PCI machine types, followed by keyboard reset for old
> QEMU + isapc.

Any chance of getting this fix into the about to be tagged stable?

Dave

> Paolo
> 
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--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK