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

[Felix Kuehling <felix.kuehling@xxxxxxx>]

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@xxxxxxx>
> > ---
> >   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);