| Message ID | b1b44823f93fd9e7fa73dc165141d716cb74fa90.1759070796.git.leon@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | vfio/pci: Allow MMIO regions to be exported through dma-buf | expand |
On Sun, 28 Sep 2025 17:50:17 +0300 Leon Romanovsky <leon@kernel.org> wrote: > From: Leon Romanovsky <leonro@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 <leonro@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? 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, Alex
On Mon, Sep 29, 2025 at 03:17:40PM -0600, Alex Williamson wrote: > On Sun, 28 Sep 2025 17:50:17 +0300 > Leon Romanovsky <leon@kernel.org> wrote: > > > From: Leon Romanovsky <leonro@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 <leonro@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 > > 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. Thanks > > Alex > >
On Tue, 30 Sep 2025 10:57:48 +0300 Leon Romanovsky <leon@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 <leon@kernel.org> wrote: > > > > > From: Leon Romanovsky <leonro@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 <leonro@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? > > 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, Alex
On Tue, Sep 30, 2025 at 10:07:58AM -0600, Alex Williamson wrote: > On Tue, 30 Sep 2025 10:57:48 +0300 > Leon Romanovsky <leon@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 <leon@kernel.org> wrote: > > > > > > > From: Leon Romanovsky <leonro@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 <leonro@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 > >
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"