Re: [Xen-devel] [Qemu-devel] [PATCH 5/5] vga-cirrus: Workaround during restore when using Xen.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

> On Thu, Nov 24, 2011 at 18:30, Stefano Stabellini
> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >
> >> @@ -2784,9 +2796,11 @@ static void cirrus_reset(void *opaque)
> >> Â  Â  Â }
> >> Â  Â  Â s->vga.cr[0x27] = s->device_id;
> >>
> >> - Â  Â /* Win2K seems to assume that the pattern buffer is at 0xff
> >> - Â  Â  Â  initially ! */
> >> - Â  Â memset(s->vga.vram_ptr, 0xff, s->real_vram_size);
> >> + Â  Â if (!runstate_check(RUN_STATE_PREMIGRATE)) {
> >> + Â  Â  Â  Â /* Win2K seems to assume that the pattern buffer is at 0xff
> >> + Â  Â  Â  Â  Â  initially ! */
> >> + Â  Â  Â  Â memset(s->vga.vram_ptr, 0xff, s->real_vram_size);
> >> + Â  Â }
> >>
> >
> > this is not too bad, I suppose that the videoram is going to be written
> > again at restore time anyway so at least it saves some cycles
> 
> Actually, I think the next time that this vram will be written again
> is, when the guest is actually "waked-up" and wrote something there.
> Otherwise, the "restore" of the vram is done before QEMU start. So,
> the memset could leave some weard stuff the screen (a white screen?).
 
So this is the succession of events:

- vga_common_init
allocates the videoram

- cirrus_reset
sets set videoram to 0xff

- load_vmstate
the old videoram is copied over, overwriting what cirrus_reset has done

therefore setting the videoram to 0xff when resuming is a waste of
efforts

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