Nouveau - Jan 2018 - grumble/gripe ... fifo: read fault ... channel 12 killed! (eternal freeze-frame)

Twice now with v4.15-rc6, my display has gone belly up.

Note: swiotlb: suppress warning when __GFP_NOWARN is set v2 is applied,
but I don't _think_ it was the first time it happened.

[ 3729.558261] nouveau 0000:01:00.0: gr: TRAP ch 2 [00ff842000 Xorg[3413]]
[ 3729.558269] nouveau 0000:01:00.0: gr: GPC0/TPC0/TEX: 80000041
[ 3729.558273] nouveau 0000:01:00.0: gr: GPC0/TPC1/TEX: 80000041
[ 3729.558277] nouveau 0000:01:00.0: gr: GPC0/TPC2/TEX: 80000041
[ 3729.558280] nouveau 0000:01:00.0: gr: GPC0/TPC3/TEX: 80000041
[ 3729.558286] nouveau 0000:01:00.0: gr: GPC1/TPC0/TEX: 80000041
[ 3729.558289] nouveau 0000:01:00.0: gr: GPC1/TPC1/TEX: 80000041
[ 3729.558293] nouveau 0000:01:00.0: gr: GPC1/TPC2/TEX: 80000041
[ 3729.558297] nouveau 0000:01:00.0: gr: GPC1/TPC3/TEX: 80000041
[ 3729.558302] nouveau 0000:01:00.0: gr: GPC2/TPC0/TEX: 80000041
[ 3729.558305] nouveau 0000:01:00.0: gr: GPC2/TPC1/TEX: 80000041
[ 3729.558309] nouveau 0000:01:00.0: gr: GPC2/TPC2/TEX: 80000041
[ 3729.558313] nouveau 0000:01:00.0: gr: GPC2/TPC3/TEX: 80000041
[ 3729.558318] nouveau 0000:01:00.0: gr: GPC3/TPC0/TEX: 80000041
[ 3729.558322] nouveau 0000:01:00.0: gr: GPC3/TPC1/TEX: 80000041
[ 3729.558325] nouveau 0000:01:00.0: gr: GPC3/TPC2/TEX: 80000041
[ 3729.558329] nouveau 0000:01:00.0: gr: GPC3/TPC3/TEX: 80000041
[ 3729.558336] nouveau 0000:01:00.0: fifo: read fault at 000a9dd000 engine 00
[GR] client 0a [GPC2/T1_3] reason 02 [PTE] on channel 2 [00ff842000 Xorg[3413]]
[ 3729.558341] nouveau 0000:01:00.0: fifo: channel 2: killed
[ 3729.558343] nouveau 0000:01:00.0: fifo: runlist 0: scheduled for recovery
[ 3729.558346] nouveau 0000:01:00.0: fifo: engine 0: scheduled for recovery
[ 3729.558352] nouveau 0000:01:00.0: fifo: engine 7: scheduled for recovery
[ 3729.558355] nouveau 0000:01:00.0: Xorg[3413]: channel 2 killed!
[ 3729.562994] nouveau 0000:01:00.0: gr: TRAP ch 12 [00fd2d6000
plasmashell[3898]]
[ 3729.563011] nouveau 0000:01:00.0: gr: GPC0/TPC0/TEX: 80000041
[ 3729.563015] nouveau 0000:01:00.0: gr: GPC0/TPC1/TEX: 80000041
[ 3729.563018] nouveau 0000:01:00.0: gr: GPC0/TPC2/TEX: 80000041
[ 3729.563022] nouveau 0000:01:00.0: gr: GPC0/TPC3/TEX: 80000041
[ 3729.563027] nouveau 0000:01:00.0: gr: GPC1/TPC0/TEX: 80000041
[ 3729.563031] nouveau 0000:01:00.0: gr: GPC1/TPC1/TEX: 80000041
[ 3729.563034] nouveau 0000:01:00.0: gr: GPC1/TPC2/TEX: 80000041
[ 3729.563038] nouveau 0000:01:00.0: gr: GPC1/TPC3/TEX: 80000041
[ 3729.563043] nouveau 0000:01:00.0: gr: GPC2/TPC0/TEX: 80000041
[ 3729.563047] nouveau 0000:01:00.0: gr: GPC2/TPC1/TEX: 80000041
[ 3729.563050] nouveau 0000:01:00.0: gr: GPC2/TPC2/TEX: 80000041
[ 3729.563054] nouveau 0000:01:00.0: gr: GPC2/TPC3/TEX: 80000041
[ 3729.563059] nouveau 0000:01:00.0: gr: GPC3/TPC0/TEX: 80000041
[ 3729.563063] nouveau 0000:01:00.0: gr: GPC3/TPC1/TEX: 80000041
[ 3729.563066] nouveau 0000:01:00.0: gr: GPC3/TPC2/TEX: 80000041
[ 3729.563070] nouveau 0000:01:00.0: gr: GPC3/TPC3/TEX: 80000041
[ 3729.563078] nouveau 0000:01:00.0: fifo: read fault at 0004be4000 engine 00
[GR] client 01 [GPC0/T1_0] reason 02 [PTE] on channel 12 [00fd2d6000
plasmashell[3898]]
[ 3729.563083] nouveau 0000:01:00.0: fifo: channel 12: killed
[ 3729.563085] nouveau 0000:01:00.0: fifo: runlist 0: scheduled for recovery
[ 3729.563089] nouveau 0000:01:00.0: fifo: engine 0: scheduled for recovery
[ 3729.563092] nouveau 0000:01:00.0: plasmashell[3898]: channel 12 killed!