Quoting Matthew Auld (2020-09-21 17:08:44)
> If we are really unlucky and encounter an error during
> i915_vm_alloc_pt_stash, we end up passing an empty pt/pd stash all the
> way down into the low-level ppgtt alloc code, leading to explosions,
> since it expects at least the required number of pt/pd for the va range.
>
> [ 211.981418] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [ 211.981421] #PF: supervisor read access in kernel mode
> [ 211.981422] #PF: error_code(0x0000) - not-present page
> [ 211.981424] PGD 80000008439cb067 P4D 80000008439cb067 PUD 84a37f067 PMD 0
> [ 211.981427] Oops: 0000 [#1] SMP PTI
> [ 211.981428] CPU: 1 PID: 1301 Comm: i915_selftest Tainted: G U I 5.9.0-rc5+ #3
> [ 211.981430] Hardware name: /NUC6i7KYB, BIOS KYSKLi70.86A.0050.2017.0831.1924 08/31/2017
> [ 211.981521] RIP: 0010:__gen8_ppgtt_alloc+0x1ed/0x3c0 [i915]
> [ 211.981523] Code: c1 48 c7 c7 5d 5d fe c0 65 ff 0d ee 1d 03 3f e8 d9 91 1f e2 8b 55 c4 31 c0 48 8b 75 b8 85 d2 0f 95 c0 48 8b 1c c6 48 89 45 98 <48> 8b 03 48 8b 90 58 02 00 00 48 85 d2 0f 84 07 ea 15 00 48 81 fa
> [ 211.981526] RSP: 0018:ffffba2cc0eb3970 EFLAGS: 00010202
> [ 211.981527] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000004
> [ 211.981529] RDX: 0000000000000002 RSI: ffff9be998bdb8c0 RDI: ffff9be99c844300
> [ 211.981530] RBP: ffffba2cc0eb39d8 R08: 0000000000000640 R09: ffff9be97cdfd000
> [ 211.981531] R10: ffff9be97cdfd614 R11: 0000000000000000 R12: 0000000000000000
> [ 211.981532] R13: ffff9be98607ba20 R14: ffff9be995a0b400 R15: ffffba2cc0eb39e8
> [ 211.981534] FS: 00007f0f10b31000(0000) GS:ffff9be99fc40000(0000) knlGS:0000000000000000
> [ 211.981536] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 211.981538] CR2: 0000000000000000 CR3: 000000084d74e006 CR4: 00000000003706e0
> [ 211.981539] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 211.981541] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 211.981542] Call Trace:
> [ 211.981609] gen8_ppgtt_alloc+0x79/0x90 [i915]
> [ 211.981678] ppgtt_bind_vma+0x36/0x80 [i915]
> [ 211.981756] __vma_bind+0x39/0x40 [i915]
> [ 211.981818] fence_work+0x21/0x98 [i915]
> [ 211.981879] fence_notify+0x8d/0x128 [i915]
> [ 211.981939] __i915_sw_fence_complete+0x62/0x240 [i915]
> [ 211.982018] i915_vma_pin_ww+0x1ee/0x9c0 [i915]
>
> Fixes: cd0452aa2a0d ("drm/i915: Preallocate stashes for vma page-directories")
> Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_vma.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 495d28f6d160..ffb5287e055a 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -892,9 +892,11 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
>
> /* Allocate enough page directories to used PTE */
> if (vma->vm->allocate_va_range) {
> - i915_vm_alloc_pt_stash(vma->vm,
> - &work->stash,
> - vma->size);
> + err = i915_vm_alloc_pt_stash(vma->vm,
> + &work->stash,
> + vma->size);
> + if (err)
> + goto err_fence;
Whelp, well that was silly of me.
Thanks,
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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