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

[Samiullah Khawaja <skhawaja@google.com>]

On Wed, May 20, 2026 at 12:57:40AM +0000, Pranjal Shrivastava wrote:
>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?

Agreed. I will update this.
>
>>
>>  	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

Thanks,
Sami