[Intel-xe] [PATCH] drm/xe: fix tlb_invalidation_seqno_past()

[Matthew Auld]

On 08/05/2023 01:53, Matthew Brost wrote:
> On Fri, May 05, 2023 at 03:49:10PM +0100, Matthew Auld wrote:
>> Checking seqno_recv >= seqno looks like it will incorrectly report true
>> when the seqno has wrapped (not unlikely given
>> TLB_INVALIDATION_SEQNO_MAX). Calling xe_gt_tlb_invalidation_wait() might
>> then return before the flush has been completed by the GuC.
>>
>> Fix this by treating a large negative delta as an indication that the
>> seqno has wrapped around. Similar to how we treat a large positive delta
>> as an indication that the seqno_recv must have wrapped around, but in
>> that case the seqno has likely also signalled.
>>
>> It looks like we could also potentially make the seqno use the full
>> 32bits as supported by the GuC.
> 
> Yea we def could use more of the space but in the end we have the seqno
> wrap issue. I think I set this to a low value to prove the wrapping
> protection worked (it didn't) by triigering wraps more often than the
> wrapping 32 bits.

Ok, make sense.

> 
> With, this patch LGTM.
> 
> Reviewed-by: Matthew Brost <matthew.brost at intel.com>

Thanks.

> 
>>
>> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
>> index 604f189dbd70..67822b3dd353 100644
>> --- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
>> +++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
>> @@ -251,14 +251,15 @@ int xe_gt_tlb_invalidation_vma(struct xe_gt *gt,
>>   
>>   static bool tlb_invalidation_seqno_past(struct xe_gt *gt, int seqno)
>>   {
>> -	if (gt->tlb_invalidation.seqno_recv >= seqno)
>> -		return true;
>> +	if (seqno - gt->tlb_invalidation.seqno_recv <
>> +	    -(TLB_INVALIDATION_SEQNO_MAX / 2))
>> +		return false;
>>   
>>   	if (seqno - gt->tlb_invalidation.seqno_recv >
>>   	    (TLB_INVALIDATION_SEQNO_MAX / 2))
>>   		return true;
>>   
>> -	return false;
>> +	return gt->tlb_invalidation.seqno_recv >= seqno;
>>   }
>>   
>>   /**
>> -- 
>> 2.40.0
>>