Re: [PATCH v1 08/10] vfio/pci: Enable peer-to-peer DMA transactions by default

[Alex Williamson <alex.williamson@redhat.com>]

On Mon,  4 Aug 2025 16:00:43 +0300
Leon Romanovsky <leon@kernel.org> wrote:

> From: Leon Romanovsky <leonro@nvidia.com>
> 
> Make sure that all VFIO PCI devices have peer-to-peer capabilities
> enables, so we would be able to export their MMIO memory through DMABUF,
> 
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 4 ++++
>  include/linux/vfio_pci_core.h    | 1 +
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 31bdb9110cc0f..df9a32d3deac9 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -28,6 +28,7 @@
>  #include <linux/nospec.h>
>  #include <linux/sched/mm.h>
>  #include <linux/iommufd.h>
> +#include <linux/pci-p2pdma.h>
>  #if IS_ENABLED(CONFIG_EEH)
>  #include <asm/eeh.h>
>  #endif
> @@ -2088,6 +2089,9 @@ int vfio_pci_core_init_dev(struct vfio_device *core_vdev)
>  	INIT_LIST_HEAD(&vdev->dummy_resources_list);
>  	INIT_LIST_HEAD(&vdev->ioeventfds_list);
>  	INIT_LIST_HEAD(&vdev->sriov_pfs_item);
> +	vdev->provider = pci_p2pdma_enable(vdev->pdev);
> +	if (IS_ERR(vdev->provider))
> +		return PTR_ERR(vdev->provider);

I think this just made all vfio-pci drivers functionally dependent on
CONFIG_PCI_P2PDMA.  Seems at best exporting a dma-buf should be
restricted if this fails.  Thanks,

Alex

>  	init_rwsem(&vdev->memory_lock);
>  	xa_init(&vdev->ctx);
>  
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index fbb472dd99b36..b017fae251811 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -94,6 +94,7 @@ struct vfio_pci_core_device {
>  	struct vfio_pci_core_device	*sriov_pf_core_dev;
>  	struct notifier_block	nb;
>  	struct rw_semaphore	memory_lock;
> +	struct p2pdma_provider  *provider;
>  };
>  
>  /* Will be exported for vfio pci drivers usage */