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

Alex Williamson
2026-02-27T00:00:42Z

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;
> + } 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;
> + }

This could maybe be incrementally cleaner in a
int vfio_pci_core_probe_reset(struct vfio_pci_core_device *vdev)
helper.

>
> - vdev->reset_works = !ret;
> pci_save_state(pdev);
> vdev->pci_saved_state = pci_store_saved_state(pdev);

Isn't this a problem too? In the first kernel we store the initial,
post reset state of the device, now we're storing some arbitrary state.
This is the state we're restore when the device is closed.

> 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

Wouldn't a forward declaration do, and the kho/abi include can be kept
out of the public header? Also should be in the previous patch?
Thanks,

Alex