Re: [PATCH v4 02/16] vfio/pci: Preserve vfio-pci device files across Live Update

[David Matlack]

On Mon, May 11, 2026 at 4:48 PM Vipin Sharma <vipinsh@xxxxxxxxxx> wrote:

> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index c12d614fc6c4..019de053f116 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -45,13 +45,15 @@ config VFIO_PCI_IGD
>
>  config VFIO_PCI_LIVEUPDATE
>         bool "VFIO PCI support for Live Update (EXPERIMENTAL)"
> -       depends on PCI_LIVEUPDATE
> +       depends on PCI_LIVEUPDATE && VFIO_DEVICE_CDEV
>         help
>           Support for preserving devices bound to vfio-pci across a Live
>           Update. This option should only be enabled by developers working on
>           implementing this support. Once enough support has landed in the
>           kernel, this option will no longer be marked EXPERIMENTAL.
>
> +         Enabling this will disable support for VFIO PCI DMA buffer.
> +
>           If you don't know what to do here, say N.
>
>  endif
> @@ -68,7 +70,7 @@ 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 VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER && !VFIO_PCI_LIVEUPDATE

Why does enabling VFIO_PCI_LIVEUPDATE require disabling
VFIO_PCI_DMABUF? I saw the cover letter says "to keep things simple",
but what specific problem does this solve or simplify?