[Intel-gfx] [PATCH] drm/i915: Fix 32b overflow check in gen8_ppgtt_alloc_page_directories

[Michel Thierry]

On 4/30/2015 3:22 PM, Ville Syrjälä wrote:
> On Thu, Apr 30, 2015 at 02:59:34PM +0100, Michel Thierry wrote:
>> The patch 69876bed7e008f5fe01538a2d47c09f2862129d0: "drm/i915/gen8:
>> page directories rework allocation" added an overflow warning, but the
>> mask had an extra 0. Use typo-prone option suggested by Dave instead.
>>
>> This check will be unnecessary after gen8_alloc_va_range handles more
>> than 4 PDPs (48b addressing).
>>
>> Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
>> Cc: Dave Gordon <david.s.gordon at intel.com>
>> Signed-off-by: Michel Thierry <michel.thierry at intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gem_gtt.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> index 6fae6bd..6d894fc 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> @@ -756,8 +756,8 @@ static int gen8_ppgtt_alloc_page_directories(struct i915_hw_ppgtt *ppgtt,
>>
>>   	WARN_ON(!bitmap_empty(new_pds, GEN8_LEGACY_PDPES));
>>
>> -	/* FIXME: PPGTT container_of won't work for 64b */
>> -	WARN_ON((start + length) > 0x800000000ULL);
>> +	/* FIXME: upper bound must not overflow 31 bits  */
>> +	WARN_ON((start + length) & (~0ULL << 31));
>
> Why is it 31 and not 32?
>

Right, the check really should be (start + length) >= 0x100000000ULL.

>>
>>   	gen8_for_each_pdpe(pd, pdp, start, length, temp, pdpe) {
>>   		if (pd)
>> --
>> 2.1.1
>>
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>