Hi David, On Thu, 12 Mar 2026 23:39:45 +0000 David Matlack <[email protected]> wrote:
> On 2026-03-09 10:32 AM, David Matlack wrote: > > On Fri, Feb 27, 2026 at 9:57 AM Alex Williamson <[email protected]> > > wrote: > > > > Sorry if I don't have the whole model in my head yet, but is > > > exposing the restriction to the vfio user of the device > > > sufficient to manage the liveupdate orchestration? For example, > > > a VFIO_DEVICE_INFO_CAP pushes the knowledge to QEMU... what does > > > QEMU do with that knowledge? Who imposes the policy decision to > > > decide what support is sufficient? > > > > Hm.. good questions. I don't think we want userspace inspecting bits > > exposed by the kernel and trying to infer exactly what's being > > preserved and whether it's "good enough" to use. And such a UAPI > > would become tech debt once we finish development, I suspect. > > > > A better approach would be to hide this support from userspace until > > we decide it is ready for production use-cases. > > > > To enable development and testing, we can add an opt-in mechanism > > Here is what I am trending towards sending in v3 as the opt-in > mechanism: > > diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig > index 1e82b44bda1a..770231554221 100644 > --- a/drivers/vfio/pci/Kconfig > +++ b/drivers/vfio/pci/Kconfig > @@ -58,6 +58,27 @@ config VFIO_PCI_ZDEV_KVM > config VFIO_PCI_DMABUF > def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER > > +config VFIO_PCI_LIVEUPDATE > + bool "VFIO PCI support for Live Update (EXPERIMENTAL)" > + depends on LIVEUPDATE && VFIO_PCI > + help > + Support for preserving devices bound to vfio-pci across a > Live > + Update. The eventual goal is that preserved devices can run > + uninterrupted during a Live Update, including DMA to > preserved > + memory buffers and P2P. However there are many steps still > needed to > + achieve this, including: > + > + - Preservation of iommufd files > + - Preservation of IOMMU driver state In the interim, what do you think about moving forward with noiommu mode without preserving IOMMU driver state? I’ve tested your vfio_pci_liveupdate_kexec_test with the noiommu cdev, and it works as expected. > + - Preservation of PCI state (BAR resources, device state, > ...) > + - Preservation of vfio-pci driver state > + > + 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. > + > + If you don't know what to do here, say N. > + > source "drivers/vfio/pci/mlx5/Kconfig" > > source "drivers/vfio/pci/hisilicon/Kconfig"
