On Tue, Sep 30, 2025 at 10:07:58AM -0600, Alex Williamson wrote: > On Tue, 30 Sep 2025 10:57:48 +0300 > Leon Romanovsky <l...@kernel.org> wrote: > > > On Mon, Sep 29, 2025 at 03:17:40PM -0600, Alex Williamson wrote: > > > On Sun, 28 Sep 2025 17:50:17 +0300 > > > Leon Romanovsky <l...@kernel.org> wrote: > > > > > > > From: Leon Romanovsky <leo...@nvidia.com> > > > > > > > > Add new kernel config which indicates support for dma-buf export > > > > of MMIO regions, which implementation is provided in next patches. > > > > > > > > Signed-off-by: Leon Romanovsky <leo...@nvidia.com> > > > > --- > > > > drivers/vfio/pci/Kconfig | 20 ++++++++++++++++++++ > > > > 1 file changed, 20 insertions(+) > > > > > > > > diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig > > > > index 2b0172f54665..55ae888bf26a 100644 > > > > --- a/drivers/vfio/pci/Kconfig > > > > +++ b/drivers/vfio/pci/Kconfig > > > > @@ -55,6 +55,26 @@ config VFIO_PCI_ZDEV_KVM > > > > > > > > To enable s390x KVM vfio-pci extensions, say Y. > > > > > > > > +config VFIO_PCI_DMABUF > > > > + bool "VFIO PCI extensions for DMA-BUF" > > > > + depends on VFIO_PCI_CORE > > > > + depends on PCI_P2PDMA && DMA_SHARED_BUFFER > > > > + default y > > > > + help > > > > + Enable support for VFIO PCI extensions that allow exporting > > > > + device MMIO regions as DMA-BUFs for peer devices to access via > > > > + peer-to-peer (P2P) DMA. > > > > + > > > > + This feature enables a VFIO-managed PCI device to export a > > > > portion > > > > + of its MMIO BAR as a DMA-BUF file descriptor, which can be > > > > passed > > > > + to other userspace drivers or kernel subsystems capable of > > > > + initiating DMA to that region. > > > > + > > > > + Say Y here if you want to enable VFIO DMABUF-based MMIO export > > > > + support for peer-to-peer DMA use cases. > > > > + > > > > + If unsure, say N. > > > > + > > > > source "drivers/vfio/pci/mlx5/Kconfig" > > > > > > > > source "drivers/vfio/pci/hisilicon/Kconfig" > > > > > > This is only necessary if we think there's a need to build a kernel with > > > P2PDMA and VFIO_PCI, but not VFIO_PCI_DMABUF. Does that need really > > > exist? > > > > It is used to filter build of vfio_pci_dmabuf.c - drivers/vfio/pci/Makefile: > > vfio-pci-core-$(CONFIG_VFIO_PCI_DMABUF) += vfio_pci_dmabuf.o > > Maybe my question of whether it needs to exist at all is too broad. > Does it need to be a user visible Kconfig option? Where do we see the > need to preclude this feature from vfio-pci if the dependencies are > enabled?
The dependencies are for the platform and not for the devices. For example, hisilicon device mentioned in other email doesn't support p2p, but the platform most likely support. I don't have strong feelings about this config and at least for our use case will always be enabled. I can hide it from the users. > > > > I also find it unusual to create the Kconfig before adding the > > > supporting code. Maybe this could be popped to the end or rolled into > > > the last patch if we decided to keep it. Thanks, > > > > It is leftover from previous version, I can squash it, but first we need > > to decide what to do with pcim_p2pdma_init() call, if it needs to be > > guarded or not. > > As in the other thread, I think it would be cleaner in an IS_ENABLED > branch. I'm tempted to suggest we filter out EOPNOTSUPP to allow it to > be unconditional, but I understand your point with the list_head > initialization. Thanks, We can add dmabuf list to struct unconditionally, as memory overhead is negligible. It will allow us to drop IS_ENABLED() too. Thanks > > Alex > >
