Re: [PATCH 2/5] drm/i915: harden allocation paths in allocate_va_range

From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
To: Matthew Auld <matthew.auld@intel.com>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 2/5] drm/i915: harden allocation paths in allocate_va_range
Date: Mon, 18 Apr 2016 16:13:27 +0300	[thread overview]
Message-ID: <1460985207.6027.5.camel@linux.intel.com> (raw)
In-Reply-To: <1460476663-24890-2-git-send-email-matthew.auld@intel.com>

On ti, 2016-04-12 at 16:57 +0100, Matthew Auld wrote:
> For the gen6/gen8_allocate_va_range functions remove the WARN_ON range
> sanity checks in favour of simply hardening the allocation paths. This
> also fixes the inconsistency in which we don't always handle the
> potential overflow in our checks.
> 

Not sure this is the right thing to do. I think I do prefer erroring
out on invalid arguments as we're talking of internal programmer
interface.

Regards, Joonas

> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 17 ++++-------------
>  1 file changed, 4 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 5ed713d..fa583d5 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -1220,15 +1220,6 @@ static int gen8_alloc_va_range_3lvl(struct i915_address_space *vm,
>  	uint32_t pdpes = I915_PDPES_PER_PDP(dev);
>  	int ret;
>  
> -	/* Wrap is never okay since we can only represent 48b, and we don't
> -	 * actually use the other side of the canonical address space.
> -	 */
> -	if (WARN_ON(start + length < start))
> -		return -ENODEV;
> -
> -	if (WARN_ON(start + length > vm->total))
> -		return -ENODEV;
> -
>  	ret = alloc_gen8_temp_bitmaps(&new_page_dirs, &new_page_tables, pdpes);
>  	if (ret)
>  		return ret;
> @@ -1370,6 +1361,8 @@ static int gen8_alloc_va_range(struct i915_address_space *vm,
>  {
>  	struct i915_hw_ppgtt *ppgtt = i915_vm_to_ppgtt(vm);
>  
> +	length = min_t(uint64_t, length, vm->total);
> +
>  	if (USES_FULL_48BIT_PPGTT(vm->dev))
>  		return gen8_alloc_va_range_4lvl(vm, &ppgtt->pml4, start, length);
>  	else
> @@ -1860,11 +1853,9 @@ static int gen6_alloc_va_range(struct i915_address_space *vm,
>  	uint32_t pde, temp;
>  	int ret;
>  
> -	if (WARN_ON(start_in + length_in > ppgtt->base.total))
> -		return -ENODEV;
> -
>  	start = start_save = start_in;
> -	length = length_save = length_in;
> +	length = length_save = length_in = min_t(uint64_t, length_in,
> +						 ppgtt->base.total);
>  
>  	bitmap_zero(new_page_tables, I915_PDES);
>  
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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