Re: [PATCH v2 10/22] vfio/pci: Skip reset of preserved device after Live Update

David Matlack
2026-03-12T23:39:56Z

On 2026-03-09 10:32 AM, David Matlack wrote:
> On Fri, Feb 27, 2026 at 9:57 AM Alex Williamson <alex@shazbot.org> 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
+ - 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"