Comment 1 for bug 891270

Relevant dmesg:

kernel: [ 64.737045] BUG: unable to handle kernel paging request at f9152470
kernel: [ 64.737060] IP: [<c12ae9d0>] iowrite32+0x30/0x40
kernel: [ 64.737070] *pdpt = 00000000018e5001 *pde = 000000002f10f067 *pte = 0000000000000000
kernel: [ 64.737078] Oops: 0002 [#1] SMP
kernel: [ 64.737084] Modules linked in: bnep rfcomm bluetooth parport_pc ppdev snd_hda_codec_realtek binfmt_misc snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq_midi arc4 snd_rawmidi snd_seq_midi_event iwlagn mac80211 snd_seq snd_timer snd_seq_device i915 cfg80211 snd soundcore snd_page_alloc drm_kms_helper drm joydev i2c_algo_bit mei(C) usbhid hid shpchp lp parport video firewire_ohci firewire_core ahci crc_itu_t libahci e1000e xhci_hcd
kernel: [ 64.737162]
kernel: [ 64.737167] Pid: 1000, comm: Xorg Tainted: G C 3.1.0-2-generic-pae #3-Ubuntu
kernel: [ 64.737182] EIP: 0060:[<c12ae9d0>] EFLAGS: 00013296 CPU: 0
kernel: [ 64.737189] EIP is at iowrite32+0x30/0x40
kernel: [ 64.737195] EAX: 13040001 EBX: f762a1a8 ECX: f9152470 EDX: f9152470
kernel: [ 64.737201] ESI: 0000000a EDI: 00000040 EBP: eea07d64 ESP: eea07d64
kernel: [ 64.737209] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
kernel: [ 64.737216] Process Xorg (pid: 1000, ti=eea06000 task=f6ff8000 task.ti=eea06000)
kernel: [ 64.737223] Stack:
kernel: [ 64.737226] eea07d70 f8bbb7a8 f762a1a8 eea07d80 f8bbe78a f762a1a8 0000000a eea07da8
kernel: [ 64.737241] f8b8ab86 ee5f94c0 eea07da0 0000000a 00000001 f762a1a8 f762a1a8 0000000a
kernel: [ 64.737255] 00000001 eea07db8 f8b8b605 00000002 00000040 eea07dd4 f8b8f5f7 f762a000
kernel: [ 64.737271] Call Trace:
kernel: [ 64.737315] [<f8bbb7a8>] blt_ring_flush.part.12+0x28/0x80 [i915]
kernel: [ 64.737337] [<f8bbe78a>] blt_ring_flush+0x7a/0xa0 [i915]
kernel: [ 64.737354] [<f8b8ab86>] i915_gem_flush_ring.part.24+0x26/0xa0 [i915]
kernel: [ 64.737367] [<f8b8b605>] i915_gem_flush_ring+0x25/0x30 [i915]
kernel: [ 64.737377] [<f8b8f5f7>] i915_gem_execbuffer_flush+0x87/0xa0 [i915]
kernel: [ 64.737387] [<f8b8fd4e>] i915_gem_execbuffer_move_to_gpu+0x11e/0x130 [i915]
kernel: [ 64.737398] [<f8b9030a>] i915_gem_do_execbuffer.isra.7+0x5aa/0x7c0 [i915]
kernel: [ 64.737405] [<c103a6af>] ? iomap_atomic_prot_pfn+0x4f/0x60
kernel: [ 64.737409] [<c103a4f4>] ? iounmap_atomic+0x64/0x90
kernel: [ 64.737423] [<f8bc4cb6>] ? i915_gem_gtt_pwrite_fast.isra.18+0xab/0xd9 [i915]
kernel: [ 64.737433] [<c112b685>] ? __kmalloc+0x195/0x1e0
kernel: [ 64.737449] [<f8b90a4d>] i915_gem_execbuffer2+0x5d/0x210 [i915]
kernel: [ 64.737458] [<c12a9fcd>] ? __copy_from_user_ll+0x2d/0x40
kernel: [ 64.737474] [<f89fdf40>] drm_ioctl+0x390/0x450 [drm]
kernel: [ 64.737501] [<f8b909f0>] ? i915_gem_execbuffer+0x4d0/0x4d0 [i915]
kernel: [ 64.737512] [<c123ff14>] ? security_file_permission+0x24/0xb0
kernel: [ 64.737537] [<f89fdbb0>] ? drm_copy_field+0x80/0x80 [drm]
kernel: [ 64.737546] [<c114b899>] do_vfs_ioctl+0x79/0x2d0
kernel: [ 64.737554] [<c10bf79d>] ? rcu_irq_exit+0xd/0x10
kernel: [ 64.737560] [<c105e24c>] ? irq_exit+0x3c/0xa0
kernel: [ 64.737575] [<c114bb5f>] sys_ioctl+0x6f/0x80
kernel: [ 64.737581] [<c157b51f>] sysenter_do_call+0x12/0x28
kernel: [ 64.737585] Code: 03 00 89 e5 89 d1 77 23 81 fa 00 00 01 00 76 0b 81 e2 ff ff 00 00 ef 5d c3 66 90 ba 44 66 73 c1 89 c8 e8 44 ff ff ff 5d c3 66 90
kernel: [ 64.737629] EIP: [<c12ae9d0>] iowrite32+0x30/0x40 SS:ESP 0068:eea07d64
kernel: [ 64.737636] CR2: 00000000f9152470
kernel: [ 64.738320] ---[ end trace dcb7c5f417583799 ]---