Re: [PATCH] drm/i915: Add checks to i915_bind_vma

[Josh Boyer]

On Wed, Apr 22, 2015 at 12:45 PM, Mika Kuoppala
<mika.kuoppala@xxxxxxxxxxxxxxx> wrote:
> The current aliasing ppgtt implementation allocates
> the page table structures on driver initialization
> for the entire vm address space. Earlier the page tables
> were allocated as array of struct pages, but introduction
> of dynamic allocation of page structures changed the page
> tables to be inside a page directory.
>
> We have a detailed bug report where traversing of tables and
> deferencing page_table[pte]->page oopses. This indicates that
> our pre allocation of page tables has failed or that we get
> corrupt vma which does not fit inside the vm area and throws
> pte > 511.
>
> Add more checks to catch the latter. Warn and bail out if
> we get vma which is out of bounds for binding.
>
> v2: Check vma node early (Chris)
>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Michel Thierry <michel.thierry@xxxxxxxxx>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 0239fbf..2ffa8f6 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -2746,6 +2746,13 @@ i915_get_ggtt_vma_pages(struct i915_vma *vma)
>  int i915_vma_bind(struct i915_vma *vma, enum i915_cache_level cache_level,
>                   u32 flags)
>  {
> +
> +       if (WARN_ON(!drm_mm_node_allocated(&vma->node)))
> +               return -EINVAL;
> +
> +       if (WARN_ON(vma->node.start > vma->vm->total - vma->node.size))
> +               return -EINVAL;
> +

Do you really need a full backtrace in these cases?  From an end user
perspective, they're going to get a popup saying they have a kernel
problem or an automated tool will file a bug for them and they will
have no idea what any of this means.

I understand the need for the check, but could it be done in a way
that doesn't splat an oops on a user's system?  The i915 driver has
tons of these kinds of WARN_ONs already and they don't seem to be
helping anything overall...

josh

>         if (i915_is_ggtt(vma->vm)) {
>                 int ret = i915_get_ggtt_vma_pages(vma);
>
> --
> 1.9.1
>
> --
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