Frame buffer mmap not working in pvops dom0

[Daniel De Graaf <dgdegra@tycho.nsa.gov>]

I'm trying to confirm the fix to the VESA fbdev mmap issue that was
brought up a few months ago
(http://marc.info/?l=xen-devel&m=126842551306571&w=2). The wiki page at
http://wiki.xensource.com/xenwiki/XenPVOPSDRM says that this bug should
be fixed, but doesn't point to a patch for the fix. I am still able to
reproduce the issue both on real hardware and by running Xen under qemu
(using cirrusfb on the dom0). Eamon (the original reporter) has also not
been able to confirm a fix.

I'm currently testing using Xen 4.1 built from hg 21831:6bebaf40e925 and
a pvops dom0 from xen/stable-2.6.32.x revid c0a00fbe.

So far, I've been able to determine that an mmap requesting multiple
pages from /dev/fb0 will result in page table entries all pointing to
the same physical page, which is not in the framebuffer address space.
Writing to the mapped page ends up corrupting parts of kernel memory.
I'd be happy to run further tests, try patches, or provide more
information if needed.

-- 

Daniel De Graaf
National Security Agency