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

[Jacob Pan <jacob.pan@linux.microsoft.com>]

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