On Wed, Jun 10, 2026 at 04:43:18PM +0100, Matt Evans wrote:
> Convert the VFIO device fd fops->mmap to create a DMABUF representing
> the BAR mapping, and make the VMA fault handler look up PFNs from the
> corresponding DMABUF. This supports future code mmap()ing BAR
> DMABUFs, and iommufd work to support Type1 P2P.
>
> First, vfio_pci_core_mmap() uses the new
> vfio_pci_core_mmap_prep_dmabuf() helper to export a DMABUF
> representing a single BAR range. Then, the vfio_pci_mmap_huge_fault()
> callback is updated to understand revoked buffers, and uses the new
> vfio_pci_dma_buf_find_pfn() helper to determine the PFN for a given
> fault address.
>
> Now that the VFIO DMABUFs can be mmap()ed, vfio_pci_dma_buf_move()
> zaps PTEs (used on the revocation and cleanup paths).
>
> CONFIG_VFIO_PCI_CORE now unconditionally depends on
> CONFIG_DMA_SHARED_BUFFER and CONFIG_PCI_P2PDMA_CORE. The
> CONFIG_VFIO_PCI_DMABUF feature conditionally includes support for
> VFIO_DEVICE_FEATURE_DMA_BUF, depending on the availability of
> CONFIG_PCI_P2PDMA.
>
> Signed-off-by: Matt Evans <[email protected]>
> ---
> drivers/vfio/pci/Kconfig | 5 +-
> drivers/vfio/pci/Makefile | 3 +-
> drivers/vfio/pci/vfio_pci_core.c | 75 +++++++++++++++++++-----------
> drivers/vfio/pci/vfio_pci_dmabuf.c | 12 +++++
> drivers/vfio/pci/vfio_pci_priv.h | 11 +----
> 5 files changed, 67 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index 296bf01e185e..67a2ae1fbc04 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -6,6 +6,8 @@ config VFIO_PCI_CORE
> tristate
> select VFIO_VIRQFD
> select IRQ_BYPASS_MANAGER
> + select PCI_P2PDMA_CORE
> + select DMA_SHARED_BUFFER
>
> config VFIO_PCI_INTX
> def_bool y if !S390
> @@ -56,7 +58,8 @@ config VFIO_PCI_ZDEV_KVM
> To enable s390x KVM vfio-pci extensions, say Y.
>
> config VFIO_PCI_DMABUF
> - def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER
> + def_bool y if PCI_P2PDMA
> + depends on VFIO_PCI_CORE
>
> source "drivers/vfio/pci/mlx5/Kconfig"
>
[...]
> int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
> struct vm_area_struct *vma,
> @@ -532,6 +538,10 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device
> *vdev, bool revoked)
> struct vfio_pci_dma_buf *tmp;
>
> lockdep_assert_held_write(&vdev->memory_lock);
> + /*
> + * Holding memory_lock ensures a racing VMA fault observes
> + * priv->revoked properly.
> + */
Nit: This comment should appear before the lockdep_assert_held_write()
Also, it is slightly verbose.. (not against it though).
>
> list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
> if (!get_file_active(&priv->dmabuf->file))
> @@ -549,6 +559,8 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device
> *vdev, bool revoked)
> if (revoked) {
> kref_put(&priv->kref, vfio_pci_dma_buf_done);
> wait_for_completion(&priv->comp);
> +
> unmap_mapping_range(priv->dmabuf->file->f_mapping,
> + 0, priv->size, 1);
Have we run this series with lockdep enabled?
I guess it'd be nice to check with lockdep once..
Apart from these,
Reviewed-by: Pranjal Shrivastava <[email protected]>
Thanks,
Praan
