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

[Gleb Natapov]

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.

--
                        Gleb.