Re: [PATCH] drm/amdkfd: correct the SVM DMA device unmap direction

[Felix Kuehling <felix.kuehling@amd.com>]

On 2024-11-05 06:04, Christian König wrote:
> Am 05.11.24 um 03:33 schrieb Prike Liang:
>> The SVM DMA device unmap direction should be same as
>> the DMA map process.
>
> At least of hand that looks like it's only papering over a major problem.
>
> Why are DMA ranges for SVM mapped with a direction in the first place? 
> That is usually not something we should do.

These are DMA mappings of system memory pages. I guess we're creating 
DMA mappings only for the access required for the migration, which is 
not bidirectional. I see we do something similar for userptr mappings 
depending on whether the GPU mapping is read-only or read-write. Is that 
wrong for userptrs as well?

Regards,
   Felix


>
> Regards,
> Christian.
>
>>
>> Signed-off-by: Prike Liang <Prike.Liang@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 4 ++--
>>   drivers/gpu/drm/amd/amdkfd/kfd_svm.c     | 6 +++---
>>   drivers/gpu/drm/amd/amdkfd/kfd_svm.h     | 3 ++-
>>   3 files changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c 
>> b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> index eacfeb32f35d..9d83bb9dd004 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
>> @@ -445,7 +445,7 @@ svm_migrate_vma_to_vram(struct kfd_node *node, 
>> struct svm_range *prange,
>>       pr_debug("successful/cpages/npages 0x%lx/0x%lx/0x%lx\n",
>>                mpages, cpages, migrate.npages);
>>   -    svm_range_dma_unmap_dev(adev->dev, scratch, 0, npages);
>> +    svm_range_dma_unmap_dev(adev->dev, scratch, 0, npages, 
>> DMA_TO_DEVICE);
>>     out_free:
>>       kvfree(buf);
>> @@ -750,7 +750,7 @@ svm_migrate_vma_to_ram(struct kfd_node *node, 
>> struct svm_range *prange,
>>       svm_migrate_copy_done(adev, mfence);
>>       migrate_vma_finalize(&migrate);
>>   -    svm_range_dma_unmap_dev(adev->dev, scratch, 0, npages);
>> +    svm_range_dma_unmap_dev(adev->dev, scratch, 0, npages, 
>> DMA_FROM_DEVICE);
>>     out_free:
>>       kvfree(buf);
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c 
>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> index 3e2911895c74..c21485fe6cbb 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> @@ -233,9 +233,9 @@ svm_range_dma_map(struct svm_range *prange, 
>> unsigned long *bitmap,
>>   }
>>     void svm_range_dma_unmap_dev(struct device *dev, dma_addr_t 
>> *dma_addr,
>> -             unsigned long offset, unsigned long npages)
>> +             unsigned long offset, unsigned long npages,
>> +                enum dma_data_direction dir)
>>   {
>> -    enum dma_data_direction dir = DMA_BIDIRECTIONAL;
>>       int i;
>>         if (!dma_addr)
>> @@ -272,7 +272,7 @@ void svm_range_dma_unmap(struct svm_range *prange)
>>           }
>>           dev = &pdd->dev->adev->pdev->dev;
>>   -        svm_range_dma_unmap_dev(dev, dma_addr, 0, prange->npages);
>> +        svm_range_dma_unmap_dev(dev, dma_addr, 0, prange->npages, 
>> DMA_BIDIRECTIONAL);
>>       }
>>   }
>>   diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.h 
>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>> index bddd24f04669..5370d68bc5b2 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>> @@ -182,7 +182,8 @@ void svm_range_add_list_work(struct 
>> svm_range_list *svms,
>>                    enum svm_work_list_ops op);
>>   void schedule_deferred_list_work(struct svm_range_list *svms);
>>   void svm_range_dma_unmap_dev(struct device *dev, dma_addr_t *dma_addr,
>> -             unsigned long offset, unsigned long npages);
>> +             unsigned long offset, unsigned long npages,
>> +             enum dma_data_direction dir);
>>   void svm_range_dma_unmap(struct svm_range *prange);
>>   int svm_range_get_info(struct kfd_process *p, uint32_t 
>> *num_svm_ranges,
>>                  uint64_t *svm_priv_data_size);
>