Re: [PATCH] drm/xe/vm: don't ignore error when in_kthread

[Matthew Auld <matthew.auld@intel.com>]

On 05/02/2024 18:41, Matthew Brost wrote:
> On Fri, Feb 02, 2024 at 05:14:36PM +0000, Matthew Auld wrote:
>> If GUP fails and we are in_kthread, we can have pinned = 0 and ret = 0.
>> If that happens we call sg_alloc_append_table_from_pages() with n_pages
>> = 0, which is not well behaved and can trigger:
>>
>> kernel BUG at include/linux/scatterlist.h:115!
>>
>> depending on if the pages array happens to be zeroed or not. Even if we
>> don't hit that it crashes later when trying to dma_map the returned
>> table.
>>
>> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Cc: Matthew Brost <matthew.brost@intel.com>
> 
> Someone from Habana point this out a while back and forgot to follow up
> on fixing this. Thanks for fixing this and looks correct.
> 
> Should we include a Fixes tag here? I am thinking so.
> 
> With a fixes tag:
> Reviewed: Matthew Brost <matthew.brost@intel.com>

Pushed with: Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver 
for Intel GPUs")

Thanks for the review.

> 
>> ---
>>   drivers/gpu/drm/xe/xe_vm.c | 5 +----
>>   1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
>> index 9c1c68a2fff7..63aeb3aead04 100644
>> --- a/drivers/gpu/drm/xe/xe_vm.c
>> +++ b/drivers/gpu/drm/xe/xe_vm.c
>> @@ -114,11 +114,8 @@ int xe_vma_userptr_pin_pages(struct xe_userptr_vma *uvma)
>>   					  num_pages - pinned,
>>   					  read_only ? 0 : FOLL_WRITE,
>>   					  &pages[pinned]);
>> -		if (ret < 0) {
>> -			if (in_kthread)
>> -				ret = 0;
>> +		if (ret < 0)
>>   			break;
>> -		}
>>   
>>   		pinned += ret;
>>   		ret = 0;
>> -- 
>> 2.43.0
>>