[PATCH] drm/ttm: Refuse to fault (prime-) imported pages

[Thomas Hellstrom]

On 01/07/2014 10:14 AM, Daniel Vetter wrote:
> On Fri, Jan 03, 2014 at 11:22:17AM +0100, Thomas Hellstrom wrote:
>> This is illegal for at least two reasons:
>>
>> 1) While it may work on some platforms / iommus, obtaining page pointers from
>> mapped sg-lists is illegal, since the DMA API allows page pointer information
>> to be destroyed in the sg mapping process.
>>
>> 2) TTM has no way of determining the linear kernel map caching state of the
>> underlying pages. PTEs with conflicting caching state pointing to the same
>> pfn is not allowed.
>>
>> TTM operations touching pages of imported sg-tables should be redirected through
>> the proper dma-buf operations.
>>
>> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> Shouldn't we do something similar in the kmap helpers ttm_bo_util.c like
> ttm_bo_kmap and ttm_bo_move_memcpy? Maybe just a BUG to catch driver bugs.
> Otherwise this sounds like the right thing to do, so Acked.
> -Daniel

Indeed, although I think that TTM should by default reroute the
ttm_bo_kmap operations through the
correct dma-buf ops. Haven't gotten around to do that yet.

/Thomas



>> ---
>>  drivers/gpu/drm/ttm/ttm_bo_vm.c |    9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> index cdda784..12d7f53 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> @@ -132,6 +132,15 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>>  		return VM_FAULT_NOPAGE;
>>  	}
>>  
>> +	/*
>> +	 * Refuse to fault imported pages. This should be handled
>> +	 * (if at all) by redirecting mmap to the exporter.
>> +	 */
>> +	if (bo->ttm && (bo->ttm->page_flags & TTM_PAGE_FLAG_SG)) {
>> +		retval = VM_FAULT_SIGBUS;
>> +		goto out_unlock;
>> +	}
>> +
>>  	if (bdev->driver->fault_reserve_notify) {
>>  		ret = bdev->driver->fault_reserve_notify(bo);
>>  		switch (ret) {
>> -- 
>> 1.7.10.4
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