Re: [PATCH v2 02/11] drm/amdkfd: Use migrate pfns internally

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

On 2026-01-07 04:18, Jordan Niethe wrote:
> A future change will remove device private pages from the physical
> address space. This will mean that device private pages no longer have a
> pfn.
>
> A MIGRATE_PFN flag will be introduced that distinguishes between mpfns
> that contain a pfn vs an offset into device private memory.
>
> Replace usages of pfns and page_to_pfn() to mpfns and
> migrate_pfn_to_page() to prepare for handling this distinction. This
> will assist in continuing to use the same code paths for both
> MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_COHERENT devices.
>
> Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
> ---
> v2:
>    - New to series
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 15 +++++++--------
>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.h |  2 +-
>   2 files changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index ca552c34ece2..c493b19268cc 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -204,17 +204,17 @@ svm_migrate_copy_done(struct amdgpu_device *adev, struct dma_fence *mfence)
>   }
>   
>   unsigned long
> -svm_migrate_addr_to_pfn(struct amdgpu_device *adev, unsigned long addr)
> +svm_migrate_addr_to_mpfn(struct amdgpu_device *adev, unsigned long addr)
>   {
> -	return (addr + adev->kfd.pgmap.range.start) >> PAGE_SHIFT;
> +	return migrate_pfn((addr + adev->kfd.pgmap.range.start) >> PAGE_SHIFT);
>   }
>   
>   static void
> -svm_migrate_get_vram_page(struct svm_range *prange, unsigned long pfn)
> +svm_migrate_get_vram_page(struct svm_range *prange, unsigned long mpfn)
>   {
>   	struct page *page;
>   
> -	page = pfn_to_page(pfn);
> +	page = migrate_pfn_to_page(mpfn);
>   	svm_range_bo_ref(prange->svm_bo);
>   	page->zone_device_data = prange->svm_bo;
>   	zone_device_page_init(page, 0);
> @@ -225,7 +225,7 @@ svm_migrate_put_vram_page(struct amdgpu_device *adev, unsigned long addr)
>   {
>   	struct page *page;
>   
> -	page = pfn_to_page(svm_migrate_addr_to_pfn(adev, addr));
> +	page = migrate_pfn_to_page(svm_migrate_addr_to_mpfn(adev, addr));
>   	unlock_page(page);
>   	put_page(page);
>   }
> @@ -235,7 +235,7 @@ svm_migrate_addr(struct amdgpu_device *adev, struct page *page)
>   {
>   	unsigned long addr;
>   
> -	addr = page_to_pfn(page) << PAGE_SHIFT;
> +	addr = (migrate_pfn_from_page(page) >> MIGRATE_PFN_SHIFT) << PAGE_SHIFT;
>   	return (addr - adev->kfd.pgmap.range.start);

I guess we rely on the fact that for DEVICE_PRIVATE memory, 
adev->kfd.pgmap.range.start will be 0 after your patch 11. So we don't 
need a special condition here to handle DEVICE_PRIVATE differently.

In general, I like the way you handle mpfns as it keeps all the special 
casing out of the drivers.

Regards,
   Felix


>   }
>   
> @@ -301,9 +301,8 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct svm_range *prange,
>   
>   		if (migrate->src[i] & MIGRATE_PFN_MIGRATE) {
>   			dst[i] = cursor.start + (j << PAGE_SHIFT);
> -			migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]);
> +			migrate->dst[i] = svm_migrate_addr_to_mpfn(adev, dst[i]);
>   			svm_migrate_get_vram_page(prange, migrate->dst[i]);
> -			migrate->dst[i] = migrate_pfn(migrate->dst[i]);
>   			mpages++;
>   		}
>   		spage = migrate_pfn_to_page(migrate->src[i]);
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.h b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.h
> index 2b7fd442d29c..a80b72abe1e0 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.h
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.h
> @@ -48,7 +48,7 @@ int svm_migrate_vram_to_ram(struct svm_range *prange, struct mm_struct *mm,
>   			    uint32_t trigger, struct page *fault_page);
>   
>   unsigned long
> -svm_migrate_addr_to_pfn(struct amdgpu_device *adev, unsigned long addr);
> +svm_migrate_addr_to_mpfn(struct amdgpu_device *adev, unsigned long addr);
>   
>   #endif /* IS_ENABLED(CONFIG_HSA_AMD_SVM) */
>