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

Alex Williamson
2025-08-06T22:02:10Z

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 */