Re: [PATCH v3 2/7] dma-buf: Always build with DMABUF_MOVE_NOTIFY

["Christian König" <christian.koenig@amd.com>]

On 1/20/26 15:07, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
> 
> DMABUF_MOVE_NOTIFY was introduced in 2018 and has been marked as
> experimental and disabled by default ever since. Six years later,
> all new importers implement this callback.
> 
> It is therefore reasonable to drop CONFIG_DMABUF_MOVE_NOTIFY and
> always build DMABUF with support for it enabled.
> 
> Suggested-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>  drivers/dma-buf/Kconfig                     | 12 ------------
>  drivers/dma-buf/dma-buf.c                   | 12 ++----------
>  drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 10 +++-------
>  drivers/gpu/drm/amd/amdkfd/Kconfig          |  2 +-
>  drivers/gpu/drm/xe/tests/xe_dma_buf.c       |  3 +--
>  drivers/gpu/drm/xe/xe_dma_buf.c             | 12 ++++--------
>  6 files changed, 11 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index b46eb8a552d7..84d5e9b24e20 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -40,18 +40,6 @@ config UDMABUF
>  	  A driver to let userspace turn memfd regions into dma-bufs.
>  	  Qemu can use this to create host dmabufs for guest framebuffers.
>  
> -config DMABUF_MOVE_NOTIFY
> -	bool "Move notify between drivers (EXPERIMENTAL)"
> -	default n
> -	depends on DMA_SHARED_BUFFER
> -	help
> -	  Don't pin buffers if the dynamic DMA-buf interface is available on
> -	  both the exporter as well as the importer. This fixes a security
> -	  problem where userspace is able to pin unrestricted amounts of memory
> -	  through DMA-buf.
> -	  This is marked experimental because we don't yet have a consistent
> -	  execution context and memory management between drivers.
> -
>  config DMABUF_DEBUG
>  	bool "DMA-BUF debug checks"
>  	depends on DMA_SHARED_BUFFER
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 59cc647bf40e..cd3b60ce4863 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -837,18 +837,10 @@ static void mangle_sg_table(struct sg_table *sg_table)
>  
>  }
>  
> -static inline bool
> -dma_buf_attachment_is_dynamic(struct dma_buf_attachment *attach)

I would rather like to keep the wrapper and even add some explanation what it means when true is returned.

Apart from that looks good to me.

Regards,
Christian.

> -{
> -	return !!attach->importer_ops;
> -}
> -
>  static bool
>  dma_buf_pin_on_map(struct dma_buf_attachment *attach)
>  {
> -	return attach->dmabuf->ops->pin &&
> -		(!dma_buf_attachment_is_dynamic(attach) ||
> -		 !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY));
> +	return attach->dmabuf->ops->pin && !attach->importer_ops;
>  }
>  
>  /**
> @@ -1124,7 +1116,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  	/*
>  	 * Importers with static attachments don't wait for fences.
>  	 */
> -	if (!dma_buf_attachment_is_dynamic(attach)) {
> +	if (!attach->importer_ops) {
>  		ret = dma_resv_wait_timeout(attach->dmabuf->resv,
>  					    DMA_RESV_USAGE_KERNEL, true,
>  					    MAX_SCHEDULE_TIMEOUT);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index 863454148b28..349215549e8f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -145,13 +145,9 @@ static int amdgpu_dma_buf_pin(struct dma_buf_attachment *attach)
>  	 * notifiers are disabled, only allow pinning in VRAM when move
>  	 * notiers are enabled.
>  	 */
> -	if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) {
> -		domains &= ~AMDGPU_GEM_DOMAIN_VRAM;
> -	} else {
> -		list_for_each_entry(attach, &dmabuf->attachments, node)
> -			if (!attach->peer2peer)
> -				domains &= ~AMDGPU_GEM_DOMAIN_VRAM;
> -	}
> +	list_for_each_entry(attach, &dmabuf->attachments, node)
> +		if (!attach->peer2peer)
> +			domains &= ~AMDGPU_GEM_DOMAIN_VRAM;
>  
>  	if (domains & AMDGPU_GEM_DOMAIN_VRAM)
>  		bo->flags |= AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
> diff --git a/drivers/gpu/drm/amd/amdkfd/Kconfig b/drivers/gpu/drm/amd/amdkfd/Kconfig
> index 16e12c9913f9..a5d7467c2f34 100644
> --- a/drivers/gpu/drm/amd/amdkfd/Kconfig
> +++ b/drivers/gpu/drm/amd/amdkfd/Kconfig
> @@ -27,7 +27,7 @@ config HSA_AMD_SVM
>  
>  config HSA_AMD_P2P
>  	bool "HSA kernel driver support for peer-to-peer for AMD GPU devices"
> -	depends on HSA_AMD && PCI_P2PDMA && DMABUF_MOVE_NOTIFY
> +	depends on HSA_AMD && PCI_P2PDMA
>  	help
>  	  Enable peer-to-peer (P2P) communication between AMD GPUs over
>  	  the PCIe bus. This can improve performance of multi-GPU compute
> diff --git a/drivers/gpu/drm/xe/tests/xe_dma_buf.c b/drivers/gpu/drm/xe/tests/xe_dma_buf.c
> index 1f2cca5c2f81..c107687ef3c0 100644
> --- a/drivers/gpu/drm/xe/tests/xe_dma_buf.c
> +++ b/drivers/gpu/drm/xe/tests/xe_dma_buf.c
> @@ -22,8 +22,7 @@ static bool p2p_enabled(struct dma_buf_test_params *params)
>  
>  static bool is_dynamic(struct dma_buf_test_params *params)
>  {
> -	return IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY) && params->attach_ops &&
> -		params->attach_ops->invalidate_mappings;
> +	return params->attach_ops && params->attach_ops->invalidate_mappings;
>  }
>  
>  static void check_residency(struct kunit *test, struct xe_bo *exported,
> diff --git a/drivers/gpu/drm/xe/xe_dma_buf.c b/drivers/gpu/drm/xe/xe_dma_buf.c
> index 1b9cd043e517..ea370cd373e9 100644
> --- a/drivers/gpu/drm/xe/xe_dma_buf.c
> +++ b/drivers/gpu/drm/xe/xe_dma_buf.c
> @@ -56,14 +56,10 @@ static int xe_dma_buf_pin(struct dma_buf_attachment *attach)
>  	bool allow_vram = true;
>  	int ret;
>  
> -	if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) {
> -		allow_vram = false;
> -	} else {
> -		list_for_each_entry(attach, &dmabuf->attachments, node) {
> -			if (!attach->peer2peer) {
> -				allow_vram = false;
> -				break;
> -			}
> +	list_for_each_entry(attach, &dmabuf->attachments, node) {
> +		if (!attach->peer2peer) {
> +			allow_vram = false;
> +			break;
>  		}
>  	}
>  
>