kern/43501: Graphics corruption when switching from X to tty on Xen HVM/Qemu CL-GD5446

[Andrew Wilcox <AWilcox%Wilcox-Tech.com@localhost>]

>Number:         43501
>Category:       kern
>Synopsis:       When changing from an X display to a regular tty, major 
>graphics corruption occurs, and I can no longer use the display, requiring a 
>reboot.
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Jun 24 06:15:00 +0000 2010
>Originator:     Andrew Wilcox
>Release:        NetBSD 5.1_RC3
>Organization:
Wilcox Technologies
>Environment:
System: NetBSD IND-WKST009.Wilcox-Tech.com 5.1_RC3 NetBSD 5.1_RC3 (GENERIC) #0: 
Sat Jun 12 20:26:01 UTC 2010 
builds%b8.netbsd.org@localhost:/home/builds/ab/netbsd-5-1-RC3/amd64/201006130031Z-obj/home/builds/ab/netbsd-5-1-RC3/src/sys/arch/amd64/compile/GENERIC
 amd64
Architecture: x86_64
Machine: amd64
vga0 at pci0 dev 2 function 0: vendor 0x1013 product 0x00b8 (rev. 0x00)
>Description:
        I am using NetBSD 5.1_RC3 on a Xen server as an HVM domU.  While 
running X, if I switch to a tty or if I exit out of X, it renders the display 
unreadable.  A screenshot of what the display looks like via VNC is available 
at:
        http://www.wilcox-tech.com/opensource/netbsd-graphics-oops.png (10.7kB)
        As you will note, the cursor is displayed as a different colour.  When 
typing, the position of the cursor changes, but no text is ever shown.  I am 
forced to use reboot.  I can use reboot -d if you would like.
>How-To-Repeat:
        Install NetBSD 5.1_RC3 on a Xen server.
        Run X.org (I used startx(1) and Xorg(1)).
        Type "exit" in the login xterm, or press ctrl+alt+f<n>.
        Expected: A console.
        Actual: Garbled display (see screenshot).
>Fix:
        Don't run X.org.