Re: [Qemu-devel] [PATCH] isapc: Shadow ISA BIOS by default

[Kevin O'Connor <kevin@koconnor.net>]

On Fri, Oct 12, 2012 at 11:29:47AM +0200, Jan Kiszka wrote:
> On 2012-10-08 20:52, Anthony Liguori wrote:
> > Jan Kiszka <jan.kiszka@siemens.com> writes:
> > 
> >> On 2012-09-11 17:53, Jan Kiszka wrote:
> >>> Our one and only BIOS depends on a writable shadowed BIOS in the ISA
> >>> range. As we have no interface to control the write property, make that
> >>> region writable by default.
> >>>
> >>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >>> ---
> >>>
> >>> This unbreaks isapc for TCG, and keep it working for KVM once it starts
> >>> supporting read-only memslots.
[...]
> >> Ping. Or already queued?
> > 
> > I've got it queued now.  Thanks.
> 
> I'm withdrawing it: This breaks Windows 95 booting. For unknown reasons,
> this nice OS decided to overwrite the F-segment during boot. That is
> fine as long as it is properly protected. But it breaks under current
> KVM and with the patch above for the isapc. So we need a firmware
> interface to enable/disable write protection for this segment in isapc
> mode, specifically as that machine targets these old OSes.

Why withdraw the patch?  With the patch and when not using isapc,
seabios will write protect the f-segment and nothing will change.
Without the patch and with isapc the machine wont boot at all, so will
never get far enough along to have Win95 crash.

That is, the patch has no harm as it only impacts isapc and with isapc
today the machine doesn't boot at all.

-Kevin