Re: [PATCH] drm/amdgpu: fix potential VM faults

["Christian König" <ckoenig.leichtzumerken-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

> If the page tables are reserved or fenced while you allocate a new one, they would not be evicted.
And exactly that's not correct. The TTM_OPT_FLAG_ALLOW_RES_EVICT flag 
allows evicting of reserved objects.

This is useful for allocating per VM BOs, but is of course completely 
fatal in all other cases.

Regards,
Christian.

Am 19.09.19 um 16:29 schrieb Kuehling, Felix:
> I'm not disagreeing with the change. Just trying to understand how this
> could have caused a VM fault. If the page tables are reserved or fenced
> while you allocate a new one, they would not be evicted. If they are not
> reserved or fenced, there should be no expectation that they stay resident.
>
> Is this related to recoverable page fault handling? Do we need some more
> generic way to handle eviction of page tables and update the parent page
> directory (invalidate the corresponding PDE)?
>
> Regards,
>     Felix
>
> On 2019-09-19 4:41, Christian König wrote:
>> When we allocate new page tables under memory
>> pressure we should not evict old ones.
>>
>> Signed-off-by: Christian König <christian.koenig@amd.com>
>> ---
>>    drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 3 ++-
>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> index 70d45d48907a..8e44ecaada35 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>> @@ -514,7 +514,8 @@ static int amdgpu_bo_do_create(struct amdgpu_device *adev,
>>    		.interruptible = (bp->type != ttm_bo_type_kernel),
>>    		.no_wait_gpu = bp->no_wait_gpu,
>>    		.resv = bp->resv,
>> -		.flags = TTM_OPT_FLAG_ALLOW_RES_EVICT
>> +		.flags = bp->type != ttm_bo_type_kernel ?
>> +			TTM_OPT_FLAG_ALLOW_RES_EVICT : 0
>>    	};
>>    	struct amdgpu_bo *bo;
>>    	unsigned long page_align, size = bp->size;

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