Re: [Xen-devel] [RFC][PATCH] Emulate instructions in vm86 mode

[Chris Wright <chrisw@xxxxxxxxxxxx>]

* Keir Fraser (Keir.Fraser@xxxxxxxxxxxx) wrote:
> On 21/9/06 19:35, "Bastian Blank" <bastian@xxxxxxxxxxxx> wrote:
> 
> > On Sat, Sep 09, 2006 at 01:15:28AM +0100, Keir Fraser wrote:
> >> That doesn't seem to make sense. It's probably worthwhile working out why
> >> you are taking that 'failsafe' path through create_bounce_frame. If you run
> >> a debug build of Xen, do you get lines of the form 'Pre-exception: xxxxxx 
> >> ->
> >> xxxxxx' in 'xm dmesg' or on the Xen emergency console?
> > 
> > Nope. In fact I'm unable to say why this happens. Is it possible that
> > you at least merge the non-failsafe part of the patch (i.e. the if
> > vm86_mode). It makes most things working.
> 
> I already applied your original patch (which adds cs<<4 to eip if in vm86
> mode). It was obviously the right thing to do.

This is breaking machines (with at least 845G) when running video
bios.  Appears it can't set the video memory size appropriately,
and therefore X exits since it doesn't have any modes that will fit
in the default 320k.  Both backing the change out and kicking back to
userspace using if(vm86_mode(regs)) goto fail;  allow X to run again.
I've tested various combos of patched and unpatched hv on 845, 945,
and 965 to find that backing out the patch breaks X on 945.  Bastian,
any further ideas on the failsafe path?

thanks,
-chris

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