[SeaBIOS] varlow/extrastack vs code

[Kevin O'Connor]

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.

-Kevin