Re: [Xen-devel] [PATCH v2 25/24] xl: Document VGA problems arising from lack of physmap dmop

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 06 October 2017 15:51
> To: Ian Jackson <Ian.Jackson@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Ross Lagerwall
> <ross.lagerwall@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Paul Durrant
> <Paul.Durrant@xxxxxxxxxx>
> Subject: Re: [PATCH v2 25/24] xl: Document VGA problems arising from lack
> of physmap dmop
> 
> On Fri, Oct 06, 2017 at 03:33:52PM +0100, Ian Jackson wrote:
> > [ extra patch, following test report from Ross ]
> >
> > Ross reports that stdvga guests do not work, and cirrus guests are
> > slow, because qemu tries to do xc_domain_add_to_physmap.  We will
> need
> > another dmop to fix this properly.
> >
> > For now, document the problem.
> >
> > Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> > Reported-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> > CC: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> > CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> > CC: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > ---
> >  docs/man/xl.cfg.pod.5.in | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/docs/man/xl.cfg.pod.5.in b/docs/man/xl.cfg.pod.5.in
> > index 8446d43..46b5ae6 100644
> > --- a/docs/man/xl.cfg.pod.5.in
> > +++ b/docs/man/xl.cfg.pod.5.in
> > @@ -2239,6 +2239,12 @@ For example, cdrom insert will fail.
> >
> >  =item
> >
> > +Domains with stdvga graphics cards to not work.
> > +Domains with cirrus vga do work,
> > +but there are performance problems with the vga console.
> > +
> 
> I don't follow. Do you imply cirrus doesn't need add_to_physmap to
> function?

I suspect what it happening is that the VRAM is not moved into the BAR, but the 
emulation in QEMU instead handles the BAR writes and then updates the VRAM in 
its current location.

  Paul

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