[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

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.


Anthony Liguori

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.