[PATCH] drm/xe: Have LRC hold VM reference

[Niranjana Vishwanathapura]

On Fri, May 23, 2025 at 08:37:43PM +0200, Maarten Lankhorst wrote:
>Hey,
>
>The patch seems like it's missing a fixes tag. Additionally, I would say it's missing a description of the bug being fixed.
>
>Because of this, I'm not entirely clear if this is the correct way to solve the problem.
>
>Looking at the code, I only see that execlists might end up with a reference on LRC, is that when the problem happens?
>
>Could you simply add XE_BO_FLAG_USER on create instead?
>

Can't use XE_BO_FLAG_USER here as that does more than just taking VM's
reference.

I have posted a new patch here that creates lrc->bo without VM.
https://patchwork.freedesktop.org/series/149616/
Can you please take a look?

Thanks,
Niranjana

>Kind regards,
>~Maarten Lankhorst
>
>On 2025-05-22 20:09, Niranjana Vishwanathapura wrote:
>> LRC's BO uses VM's dma_resv object. Have LRC hold
>> VM reference.
>>
>> Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
>> Reviewed-by: Stuart Summers <stuart.summers at intel.com>
>> ---
>>  drivers/gpu/drm/xe/xe_lrc.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_lrc.c b/drivers/gpu/drm/xe/xe_lrc.c
>> index 61a2e87990a9..efdf4ef35b35 100644
>> --- a/drivers/gpu/drm/xe/xe_lrc.c
>> +++ b/drivers/gpu/drm/xe/xe_lrc.c
>> @@ -908,12 +908,17 @@ static void xe_lrc_set_ppgtt(struct xe_lrc *lrc, struct xe_vm *vm)
>>
>>  static void xe_lrc_finish(struct xe_lrc *lrc)
>>  {
>> +	struct xe_vm *vm = lrc->bo->vm;
>> +
>>  	xe_hw_fence_ctx_finish(&lrc->fence_ctx);
>>  	xe_bo_lock(lrc->bo, false);
>>  	xe_bo_unpin(lrc->bo);
>>  	xe_bo_unlock(lrc->bo);
>>  	xe_bo_put(lrc->bo);
>>  	xe_bo_unpin_map_no_vm(lrc->bb_per_ctx_bo);
>> +
>> +	if (vm)
>> +		xe_vm_put(vm);
>>  }
>>
>>  /*
>> @@ -1013,6 +1018,10 @@ static int xe_lrc_init(struct xe_lrc *lrc, struct xe_hw_engine *hwe,
>>  	if (IS_ERR(lrc->bo))
>>  		return PTR_ERR(lrc->bo);
>>
>> +	/* The lrc->bo uses VM's dma_resv object, take VM reference */
>> +	if (vm)
>> +		xe_vm_get(vm);
>> +
>>  	lrc->bb_per_ctx_bo = xe_bo_create_pin_map(xe, tile, NULL, SZ_4K,
>>  						  ttm_bo_type_kernel,
>>  						  bo_flags);
>