Re: tracking P->V for unmanaged device pages

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Tue, 14 Apr 2015 21:57:03 +0200
   From: Reinoud Zandijk <reinoud%NetBSD.org@localhost>

   I got a panic here:
   Apr 14 21:18:10 diablo savecore: reboot after panic: panic: kernel diagnostic
   assertion "(bo->mem.bus.base & (PAGE_SIZE - 1)) == 0" failed: file
   "../../../../external/bsd/drm2/dist/drm/ttm/ttm_bo.c", line 1618 bo bus base
   addr not page-aligned: fffffe833a3989b0

Known problem, not sure why we're getting some random kernel pointer
instead of a page-aligned bus address here.  Kasserts around the
initialization of these things suggest the objects are getting
corrupted somewhere.