drm/i915/ppgtt: Pin page directories before allocation

Commit e2b763caa6eb ("drm/i915: Remove bitmap tracking for used-pdpes")
believed that because it did not insert its freshly allocated page
directory into the pd tree, it was safe from the shrinker. I failed to
heed the lesson learnt from commit dd19674bacba ("drm/i915: Remove bitmap
tracking for used-ptes") that we need to pin all the levels in the tree
before hitting the shrinker or else the shrinker may free an upper layer
as we proceed to allocate the tree. Thus leaving dangling pointers
everywhere and a GPF should we hit direct reclaim at just the wrong
moment.

CPU: 0 PID: 7374 Comm: chromium Tainted: P           O    4.14.13-1-ARCH #1
Hardware name: Apple Inc. MacBookPro12,1/Mac-E43C1C25D4880AD6, BIOS MBP121.88Z.0167.B33.1706181928 06/18/2017
task: ffff994f696c2c40 task.stack: ffffb1a789d4c000
RIP: 0010:gen8_ppgtt_set_pde.isra.40+0x48/0x70 [i915]
RSP: 0018:ffffb1a789d4f940 EFLAGS: 00010206
RAX: 81c1788cc4f68138 RBX: ffff994f54db8000 RCX: ffff994f696c2c40
RDX: 000000023bc73003 RSI: ffff994d598b6b80 RDI: ffff994f54db8000
RBP: ffff994d598b6b80 R08: 0000000000000000 R09: 0000000000000000
R10: ffffb1a789d4f550 R11: ffff994eaf3c3208 R12: 0000000000000027
R13: 0000000000005000 R14: 0000000004e8f000 R15: ffff994f54dba000
FS:  00007f585886aa00(0000) GS:ffff994faec00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004ac8e8 CR3: 00000002552c8004 CR4: 00000000003606f0
Call Trace:
 gen8_ppgtt_alloc_pdp+0x178/0x320 [i915]
 gen8_ppgtt_alloc_4lvl+0x5f/0x150 [i915]
 ppgtt_bind_vma+0x30/0x70 [i915]
 i915_vma_bind+0x68/0xd0 [i915]
 __i915_vma_do_pin+0x2d6/0x3a0 [i915]
 eb_lookup_vmas+0x7a2/0xb50 [i915]
 i915_gem_do_execbuffer+0x4d7/0x10e0 [i915]
 ? sock_wfree+0x34/0x60
 ? unix_stream_read_generic+0x1f9/0x7e0
 ? import_iovec+0x37/0xd0
 ? i915_gem_execbuffer2+0x5d/0x390 [i915]
 i915_gem_execbuffer2+0x1b7/0x390 [i915]
 ? i915_gem_execbuffer+0x2d0/0x2d0 [i915]
 drm_ioctl_kernel+0x59/0xb0 [drm]
 drm_ioctl+0x2d5/0x370 [drm]
 ? i915_gem_execbuffer+0x2d0/0x2d0 [i915]
 ? __seccomp_filter+0x3b/0x260
 do_vfs_ioctl+0xa1/0x610
 ? syscall_trace_enter+0xdb/0x2b0
 SyS_ioctl+0x74/0x80
 do_syscall_64+0x55/0x110
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x7f584fa82d27
RSP: 002b:00007ffee14a7828 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000003b0126a1030 RCX: 00007f584fa82d27
RDX: 00007ffee14a7870 RSI: 0000000040406469 RDI: 0000000000000080
RBP: 00007ffee14a7870 R08: 0000000000000002 R09: 0000000000000077
R10: 00007f5839f2b780 R11: 0000000000000246 R12: 0000000040406469
R13: 0000000000000080 R14: 00007f5842b00040 R15: 0000000000000000
Code: 01 00 83 81 58 0a 00 00 01 48 2b 05 13 9d fd c9 48 c1 f8 06 48 c1 e0 0c 48 8d 04 d0 48 8b 56 08 48 03 05 0c 9d fd c9 48 83 ca 03 <48> 89 10 83 a9 58 0a 00 00 01 65 ff 0d 37 03 fb 3e 74 02 f3 c3
RIP: gen8_ppgtt_set_pde.isra.40+0x48/0x70 [i915] RSP: ffffb1a789d4f940

Reported-by: Eric Blau <eblau@eblau.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104773
Fixes: e2b763caa6eb ("drm/i915: Remove bitmap tracking for used-pdpes")
References: dd19674bacba ("drm/i915: Remove bitmap tracking for used-ptes")
Testcase: igt/drv_selftest/live_gtt (igt_ppgtt_shrink_boom)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180131214440.7141-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1356,15 +1356,18 @@ static int gen8_ppgtt_alloc_pd(struct i915_address_space *vm,
 		int count = gen8_pte_count(start, length);
 
 		if (pt == vm->scratch_pt) {
+			pd->used_pdes++;
+
 			pt = alloc_pt(vm);
-			if (IS_ERR(pt))
+			if (IS_ERR(pt)) {
+				pd->used_pdes--;
 				goto unwind;
+			}
 
 			if (count < GEN8_PTES || intel_vgpu_active(vm->i915))
 				gen8_initialize_pt(vm, pt);
 
 			gen8_ppgtt_set_pde(vm, pd, pt, pde);
-			pd->used_pdes++;
 			GEM_BUG_ON(pd->used_pdes > I915_PDES);
 		}
 
@@ -1388,13 +1391,16 @@ static int gen8_ppgtt_alloc_pdp(struct i915_address_space *vm,
 
 	gen8_for_each_pdpe(pd, pdp, start, length, pdpe) {
 		if (pd == vm->scratch_pd) {
+			pdp->used_pdpes++;
+
 			pd = alloc_pd(vm);
-			if (IS_ERR(pd))
+			if (IS_ERR(pd)) {
+				pdp->used_pdpes--;
 				goto unwind;
+			}
 
 			gen8_initialize_pd(vm, pd);
 			gen8_ppgtt_set_pdpe(vm, pdp, pd, pdpe);
-			pdp->used_pdpes++;
 			GEM_BUG_ON(pdp->used_pdpes > i915_pdpes_per_pdp(vm));
 
 			mark_tlbs_dirty(i915_vm_to_ppgtt(vm));