[SeaBIOS] reboot fails with QEMU "isapc" machine type

[Kevin O'Connor]

On Mon, Feb 26, 2018 at 06:08:43PM +0000, Daniel P. Berrangé wrote:
> On Thu, Feb 22, 2018 at 08:40:09PM -0500, Kevin O'Connor wrote:
> > On Mon, Feb 05, 2018 at 12:46:41PM +0000, Daniel P. Berrangé wrote:
> > > I was experimenting with old MS-DOS 6.22 under QEMU with the 'isapc' machine
> > > type, and found it is not able to reboot the guest. Bisecting QEMU blamed
> > > the QEMU change that rebased from "rel-1.9.3", to "rel-1.10.0". Further
> > > bisecting SeaBIOS blames this change:
> > > 
> > >   commit b837e68d5a6c1a5945513f1995875445a1594c8a (refs/bisect/bad)
> > >   Author: Kevin O'Connor <kevin at koconnor.net>
> > >   Date:   Mon Nov 9 15:00:19 2015 -0500
> > > 
> > >     resume: Make KVM soft reboot loop detection more flexible
> > >     
> > >     Move the check for soft reboot loops from resume.c to shadow.c and
> > >     directly check for the case where the copy of the BIOS in flash
> > >     appears to be a memory alias instead.  This prevents a hang if an
> > >     external reboot request occurs during the BIOS memcpy.
> > >     
> > >     Signed-off-by: Kevin O'Connor <kevin at koconnor.net>
> > > 
> > > I was testing as follows:
> > > 
> > >   $ qemu-system-x86_64 -machine isapc -monitor stdio demo.img
> > 
> > I finally got this to work locally.  Apparently the isapc machine type
> > requires a rom that is 128K in size.
> > 
> > This does appear to be a regression.  I think the patch below should
> > fix it.
> 
> Thanks, I've tested this patch and confirm it fixes the behaviour
> I've been seeing.

Thanks.  I committed this patch.

-Kevin