Re: [PATCH 2/2] drm/i915: Limit the scattergather coalescing to 32bits

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 2/2] drm/i915: Limit the scattergather coalescing to 32bits
Date: Fri, 14 Oct 2016 16:38:35 +0100	[thread overview]
Message-ID: <bb44575e-698d-3ab0-5495-be5205063cf2@linux.intel.com> (raw)
In-Reply-To: <20161014151811.26513-2-chris@chris-wilson.co.uk>

On 14/10/2016 16:18, Chris Wilson wrote:
> The scattergather list uses a 32bit size counter, we should avoid
> exceeding it.
>
> Fixes: 871dfbd67d4e ("drm/i915: Allow compaction upto SWIOTLB max segment size")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0d1dc04302ec..858569419134 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2238,7 +2238,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
>   
>   	max_segment = swiotlb_max_size();
>   	if (!max_segment)
> -		max_segment = obj->base.size;
> +		max_segment = rounddown(UINT_MAX, PAGE_SIZE);
>   
>   	st = kmalloc(sizeof(*st), GFP_KERNEL);
>   	if (st == NULL)

I suppose it could be possible to get more that 4GiB of of contiguous pages.

sg_alloc_table_from_pages seems broken as well, for this, and more so, 
for using longs and stuffing them into ints.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

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