Re: [Xen-devel] [PATCH v4 0/6] save/restore on Xen

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

On 01/24/2012 05:52 AM, Stefano Stabellini wrote:
> On Tue, 24 Jan 2012, Avi Kivity wrote:
> > On 01/24/2012 01:27 PM, Paolo Bonzini wrote:
> > > On 01/24/2012 12:10 PM, Avi Kivity wrote:
> > > > > But viewing RAM as just another device, having Xen only restore a
> > > > > subset of devices should be a reasonable thing to do moving forward.
> > > > > The main problem here I believe is that we have part of the VGA Bios
> > > > > functionality in the hardware emulation.
> > > > Doesn't the main BIOS clear the screen first thing at boot?  Not even
> > > > sure the reset is needed.
> > > Clearing the screen should only write to the RAM at 0xB8000 (and
> > > perhaps 0xA0000 since IIRC it's where text-mode fonts lie).  The
> > > option ROM cannot even assume that the main BIOS knows about the VESA
> > > framebuffer, can it?
> > Yes, but why should anything else be needed?
> >
> > When you switch to a graphics mode, clear as much of the framebuffer as
> > you need.
> After installing Win2K, I managed to reproduce the issue with the old
> qemu-xen and rombios (removing the memset in the vga emulator).
> However I cannot reproduce the issue with upstream qemu and seabios
> (even if I remove the memset).
>
> I think that the memset was a workaround a bug in rombios, hence it is
> not needed anymore.
>
> Removing the cirrus_vga memset would solve the main issue we have left
> with save/restore on Xen.
> However it wouldn't solve the problem for QXL: as Gerd pointed out, QXL
> needs a reset to initialize some memory regions, so another "if we are
> restoring don't do that" would be required to make it work on Xen...
I believe this is a bug in QXL (or misdesign).  It should move this logic into 
the VGA Bios.
Regards,

Anthony Liguori

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