Re: [PATCH v2 15/16] vfio/pci: Preserve the iommufd state of the vfio cdev

[Pranjal Shrivastava <praan@google.com>]

On Mon, Apr 27, 2026 at 05:56:32PM +0000, Samiullah Khawaja wrote:
> If the vfio cdev is attached to an iommufd, preserve the state of the
> attached iommufd also. Basically preserve the iommu specific state of
> the device and also the attach iommu HW unit.
> 
> Once the device and its iommufd attachment is preserved, it cannot be
> detached or attached to another IOAS until it is unpreserved.
> 
> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
> ---
>  drivers/vfio/device_cdev.c             | 10 ++++++++
>  drivers/vfio/pci/vfio_pci_liveupdate.c | 33 +++++++++++++++++++++++++-
>  2 files changed, 42 insertions(+), 1 deletion(-)
> 

[...]

> diff --git a/drivers/vfio/pci/vfio_pci_liveupdate.c b/drivers/vfio/pci/vfio_pci_liveupdate.c
> index 976ef17e6103..b56d80379ffc 100644
> --- a/drivers/vfio/pci/vfio_pci_liveupdate.c
> +++ b/drivers/vfio/pci/vfio_pci_liveupdate.c
> @@ -108,10 +108,13 @@
>  #include <linux/kho/abi/vfio_pci.h>
>  #include <linux/liveupdate.h>
>  #include <linux/errno.h>
> +#include <linux/iommufd.h>
>  #include <linux/vfio.h>
>  
>  #include "vfio_pci_priv.h"
>  
> +MODULE_IMPORT_NS("IOMMUFD");
> +
>  static bool vfio_pci_liveupdate_can_preserve(struct liveupdate_file_handler *handler,
>  					     struct file *file)
>  {
> @@ -153,9 +156,26 @@ static int vfio_pci_liveupdate_preserve(struct liveupdate_file_op_args *args)
>  	vdev = container_of(device, struct vfio_pci_core_device, vdev);
>  	pdev = vdev->pdev;
>  
> +#ifdef CONFIG_IOMMU_LIVEUPDATE
> +	/* If iommufd is attached, preserve the underlying domain */
> +	mutex_lock(&device->dev_set->lock);
> +	if (device->iommufd_attached) {
> +		u64 token, preserved_state;
> +
> +		ret = iommufd_device_preserve(args->session,
> +					      device->iommufd_device,
> +					      &token, &preserved_state);
> +		if (ret) {
> +			mutex_unlock(&device->dev_set->lock);
> +			return ret;
> +		}
> +	}
> +	mutex_unlock(&device->dev_set->lock);
> +#endif
> +
>  	ret = pci_liveupdate_preserve(pdev);
>  	if (ret)
> -		return ret;
> +		goto err_iommufd_unpreserve;

Nit: Would we hit the WARN in patch 14 if (device->iommufd_attached) was
false here? Should we check if (device->iommufd_attached) below before
calling unpreserve?

>  
>  	ser = kho_alloc_preserve(sizeof(*ser));
>  	if (IS_ERR(ser)) {
> @@ -170,6 +190,9 @@ static int vfio_pci_liveupdate_preserve(struct liveupdate_file_op_args *args)
>  	args->serialized_data = virt_to_phys(ser);
>  	return 0;
>  
> +err_iommufd_unpreserve:
> +	iommufd_device_unpreserve(args->session, device->iommufd_device);
> +
>  err_unpreserve:
>  	pci_liveupdate_unpreserve(pdev);
>  	return ret;

With that nit:

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan