[Intel-gfx] [PATCH] drm/i915: Enforce execobject.alignment to be a power-of-two

[Damien Lespiau]

On Fri, Jun 19, 2015 at 01:59:46PM +0100, Chris Wilson wrote:
> Internal requirement for the alignment is that it must be a
> power-of-two, so enforce rejection at the user interface to execbuffer
> (which allows the caller to specify a stricter-than-expected alignment
> criterion).
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

That sounds right in general and I could find at least one instance
where we rely on alignment being a power of two (eb_vma_misplaced() and
vma->node.start & (entry->alignment - 1))

so:

Reviewed-by: Damien Lespiau <damien.lespiau at intel.com>

-- 
Damien

> ---
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index f4fb2bd33753..b14733908d8d 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1189,6 +1189,9 @@ validate_exec_list(const struct drm_i915_gem_execbuffer2 *args,
>  		if (exec[i].flags & invalid_flags)
>  			return -EINVAL;
>  
> +		if (exec[i].alignment && !is_power_of_2(exec[i].alignment))
> +			return -EINVAL;
> +
>  		/* pad_to_size was once a reserved field, so sanitize it */
>  		if (exec[i].flags & EXEC_OBJECT_PAD_TO_SIZE) {
>  			if (offset_in_page(exec[i].pad_to_size))
> -- 
> 2.1.4
> 
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