Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios

[Jamie Lokier]

Gleb Natapov wrote:
> On Mon, Nov 23, 2009 at 10:30:56PM +0100, Sebastian Herbszt wrote:
> > Gleb Natapov wrote:
> > >On Mon, Nov 23, 2009 at 08:19:54PM +0100, Sebastian Herbszt wrote:
> > >>Gleb Natapov wrote:
> > >>>On Sun, Nov 22, 2009 at 09:01:45PM +0100, Sebastian Herbszt wrote:
> > >>>>Gleb Natapov wrote:
> > >>>>>On Sun, Nov 22, 2009 at 04:31:24PM +0100, Sebastian Herbszt wrote:
> > >>>>>>
> > >>>>>>Bad things could happen if someone modifies the BIOS because it's 
> > >>>>>>unprotected
> > >>>>>>(e.g. VM crash).
> > >>>>>>
> > >>>>>BIOS is reloaded during VM reset.
> > >>>>
> > >>>>The BIOS is not reloaded - tested with "reboot" on Linux and 
> > >>>>system_reset in monitor.
> > >>>>
> > >>>Looks like a bug. Tested with latest QEMU version I assume?
> > >>
> > >>Tested with v0.11.0-rc0-1677-gf165b53. Where do you suspect a bug? In the 
> > >>behaviour
> > >>on "reboot" or system_reset? I think it depends wheter it's a software or 
> > >>hardware reset.
> > >>
> > >The bug is that BIOS rom is not reloaded on hardware reset (what do you
> > >call software reset?). Can you retest with latest git?
> > 
> > Same with v0.11.0-rc0-1699-gb0293e5.
> > Bochs has the notion of BX_RESET_SOFTWARE and BX_RESET_HARDWARE. Those
> > two describe the source of the reset and the hardware, in most cases just 
> > the cpu, is reset
> > differently depending on the source (e.g. hardware reset / power on vs. 
> > INIT#). I think this
> > behaviour is also described in the 440fx spec (chapter "4.5.3 SYSTEM 
> > RESET").
> > 
> > If the monitor command "system_reset" is supposed to be the equivalent of 
> > pushing the reset
> > button of the box, then the bios should be reloaded (i think, not entirely 
> > sure what the pin is
> > wired to). But the bios should not be reloaded if the OS just jumps to the 
> > bios reset code.
> > 
> Correct, but modern OSes never jump to the bios reset code. They use
> ACPI reset, kbd reset or triple fault to do reset. All of those generate
> exactly the same kind of reset as "system_reset" monitor command.

Modern OSes don't (though Linux still has the option reboot=bios which
jumps to the BIOS reset code, because that's needed on some PCs!).

But QEMU is used to run old OSes too.

-- Jamie