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

Jacob Pan
2026-01-29T22:22:01Z

Hi David,

On Thu, 29 Jan 2026 21:24:57 +0000
David Matlack <dmatlack@google.com> wrote:

> From: Vipin Sharma <vipinsh@google.com>
>
> Do not reset the device when a Live Update preserved vfio-pci device
> is retrieved and first enabled. vfio_pci_liveupdate_freeze()
> guarantees the device is reset prior to Live Update, so there's no
> reason to reset it again after Live Update.
>
> Since VFIO normally uses the initial reset to detect if the device
> supports function resets, pass that from the previous kernel via
> struct vfio_pci_core_dev_ser.
>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
> drivers/vfio/pci/vfio_pci_core.c | 22 +++++++++++++++++-----
> drivers/vfio/pci/vfio_pci_liveupdate.c | 1 +
> include/linux/kho/abi/vfio_pci.h | 2 ++
> include/linux/vfio_pci_core.h | 1 +
> 4 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c
> b/drivers/vfio/pci/vfio_pci_core.c index b01b94d81e28..c9f73f597797
> 100644 --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -515,12 +515,24 @@ int vfio_pci_core_enable(struct
> vfio_pci_core_device *vdev) if (ret)
> goto out_power;
>
> - /* If reset fails because of the device lock, fail this path
> entirely */
> - ret = pci_try_reset_function(pdev);
> - if (ret == -EAGAIN)
> - goto out_disable_device;
> + if (vdev->liveupdate_incoming_state) {
> + /*
> + * This device was preserved by the previous kernel
> across a
> + * Live Update, so it does not need to be reset.
> + */
> + vdev->reset_works =
> vdev->liveupdate_incoming_state->reset_works;
Just wondering what happened to skipping the bus master clearing. I
understand this version does not preserve the device itself yet; I’m
just curious whether there were specific difficulties that led to
dropping the earlier patch which skipped clearing bus master.

> + } else {
> + /*
> + * If reset fails because of the device lock, fail
> this path
> + * entirely.
> + */
> + ret = pci_try_reset_function(pdev);
> + if (ret == -EAGAIN)
> + goto out_disable_device;
> +
> + vdev->reset_works = !ret;
> + }
>
> - vdev->reset_works = !ret;
> pci_save_state(pdev);
> vdev->pci_saved_state = pci_store_saved_state(pdev);
> if (!vdev->pci_saved_state)
> diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c
> b/drivers/vfio/pci/vfio_pci_liveupdate.c index
> 1ad7379c70c4..c52d6bdb455f 100644 ---
> a/drivers/vfio/pci/vfio_pci_liveupdate.c +++
> b/drivers/vfio/pci/vfio_pci_liveupdate.c @@ -57,6 +57,7 @@ static int
> vfio_pci_liveupdate_preserve(struct liveupdate_file_op_args *args)
> ser->bdf = pci_dev_id(pdev);
> ser->domain = pci_domain_nr(pdev->bus);
> + ser->reset_works = vdev->reset_works;
>
> args->serialized_data = virt_to_phys(ser);
> return 0;
> diff --git a/include/linux/kho/abi/vfio_pci.h
> b/include/linux/kho/abi/vfio_pci.h index 9bf58a2f3820..6c3d3c6dfc09
> 100644 --- a/include/linux/kho/abi/vfio_pci.h
> +++ b/include/linux/kho/abi/vfio_pci.h
> @@ -34,10 +34,12 @@
> *
> * @bdf: The device's PCI bus, device, and function number.
> * @domain: The device's PCI domain number (segment).
> + * @reset_works: Non-zero if the device supports function resets.
> */
> struct vfio_pci_core_device_ser {
> u16 bdf;
> u16 domain;
> + u8 reset_works;
> } __packed;
>
> #endif /* _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H */
> diff --git a/include/linux/vfio_pci_core.h
> b/include/linux/vfio_pci_core.h index 350c30f84a13..95835298e29e
> 100644 --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -16,6 +16,7 @@
> #include <linux/types.h>
> #include <linux/uuid.h>
> #include <linux/notifier.h>
> +#include <linux/kho/abi/vfio_pci.h>
>
> #ifndef VFIO_PCI_CORE_H
> #define VFIO_PCI_CORE_H