[PATCH] drm/ttm: Restore ttm prefaulting

[Thomas Hellström (VMware)]

On 9/13/19 12:53 PM, Koenig, Christian wrote:
> Am 12.09.19 um 20:38 schrieb Thomas Hellström (VMware):
>> From: Thomas Hellstrom <thellstrom at vmware.com>
>>
>> Commit 4daa4fba3a38 ("gpu: drm: ttm: Adding new return type vm_fault_t")
>> broke TTM prefaulting. Since vmf_insert_mixed() typically always returns
>> VM_FAULT_NOPAGE, prefaulting stops after the second PTE.
>>
>> Restore (almost) the original behaviour. Unfortunately we can no longer
>> with the new vm_fault_t return type determine whether a prefaulting
>> PTE insertion hit an already populated PTE, and terminate the insertion
>> loop. Instead we continue with the pre-determined number of prefaults.
>>
>> Fixes: 4daa4fba3a38 ("gpu: drm: ttm: Adding new return type vm_fault_t")
>> Cc: Souptick Joarder <jrdr.linux at gmail.com>
>> Cc: Christian König <christian.koenig at amd.com>
>> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> Reviewed-by: Christian König <christian.koenig at amd.com>
>
> Going to pick that up when Alex rebases our upstream branch.
>
> Christian.
>
>> ---
>>    drivers/gpu/drm/ttm/ttm_bo_vm.c | 16 +++++++---------
>>    1 file changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> index 5a580adeb9d1..aa18e8a53727 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> @@ -290,15 +290,13 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>>    		else
>>    			ret = vmf_insert_pfn(&cvma, address, pfn);
>>    
>> -		/*
>> -		 * Somebody beat us to this PTE or prefaulting to
>> -		 * an already populated PTE, or prefaulting error.
>> -		 */
>> -
>> -		if (unlikely((ret == VM_FAULT_NOPAGE && i > 0)))
>> -			break;
>> -		else if (unlikely(ret & VM_FAULT_ERROR))
>> -			goto out_io_unlock;
>> +		/* Never error on prefaulted PTEs */
>> +		if (unlikely((ret & VM_FAULT_ERROR))) {
>> +			if (i == 0)
>> +				goto out_io_unlock;
>> +			else

We could perhaps skip that else. Let me know if you want me to respin.

/Thomas



>> +				break;
>> +		}
>>    
>>    		address += PAGE_SIZE;
>>    		if (unlikely(++page_offset >= page_last))