Re: [PATCH 12/14] iommufd: Add APIs to preserve/unpreserve a vfio cdev

[Samiullah Khawaja <skhawaja@google.com>]

On Wed, Mar 25, 2026 at 08:24:24PM +0000, Pranjal Shrivastava wrote:
>On Tue, Feb 03, 2026 at 10:09:46PM +0000, Samiullah Khawaja wrote:
>> Add APIs that can be used to preserve and unpreserve a vfio cdev. Use
>> the APIs exported by the IOMMU core to preserve/unpreserve device. Pass
>> the LUO preservation token of the attached iommufd into IOMMU preserve
>> device API. This establishes the ownership of the device with the
>> preserved iommufd.
>>
>> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
>> ---
>>  drivers/iommu/iommufd/device.c | 69 ++++++++++++++++++++++++++++++++++
>>  include/linux/iommufd.h        | 23 ++++++++++++
>>  2 files changed, 92 insertions(+)
>>
>> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
>> index 4c842368289f..30cb5218093b 100644
>> --- a/drivers/iommu/iommufd/device.c
>> +++ b/drivers/iommu/iommufd/device.c
>> @@ -2,6 +2,7 @@
>>  /* Copyright (c) 2021-2022, NVIDIA CORPORATION & AFFILIATES
>>   */
>>  #include <linux/iommu.h>
>> +#include <linux/iommu-lu.h>
>>  #include <linux/iommufd.h>
>>  #include <linux/pci-ats.h>
>>  #include <linux/slab.h>
>> @@ -1661,3 +1662,71 @@ int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
>>  	iommufd_put_object(ucmd->ictx, &idev->obj);
>>  	return rc;
>>  }
>> +
>> +#ifdef CONFIG_IOMMU_LIVEUPDATE
>> +int iommufd_device_preserve(struct liveupdate_session *s,
>> +			    struct iommufd_device *idev,
>> +			    u64 *tokenp)
>> +{
>> +	struct iommufd_group *igroup = idev->igroup;
>> +	struct iommufd_hwpt_paging *hwpt_paging;
>> +	struct iommufd_hw_pagetable *hwpt;
>> +	struct iommufd_attach *attach;
>> +	int ret;
>> +
>> +	mutex_lock(&igroup->lock);
>> +	attach = xa_load(&igroup->pasid_attach, IOMMU_NO_PASID);
>
>By explicitly looking up IOMMU_NO_PASID, we skip any PASID attachments
>the device might have. Since PASID live update is NOT supported in this
>series, should we check if the pasid_attach xarray contains anything
>other than IOMMU_NO_PASID and return -EOPNOTSUPP?
>
>Otherwise, we silently fail to preserve those domains without informing
>the VMM?

VMM should be able to preserve the NO_PASID domains even if it has PASID
attachments. This is the intended behaviour, I will document it in the
uAPI docs.
>
>> +	if (!attach) {
>> +		ret = -ENOENT;
>> +		goto out;
>> +	}
>> +
>> +	hwpt = attach->hwpt;
>> +	hwpt_paging = find_hwpt_paging(hwpt);
>> +	if (!hwpt_paging || !hwpt_paging->lu_preserve) {
>> +		ret = -EINVAL;
>> +		goto out;
>> +	}
>> +
>> +	ret = liveupdate_get_token_outgoing(s, idev->ictx->file, tokenp);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = iommu_preserve_device(hwpt_paging->common.domain,
>> +				    idev->dev,
>> +				    *tokenp);
>> +out:
>> +	mutex_unlock(&igroup->lock);
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(iommufd_device_preserve, "IOMMUFD");
>> +
>> +void iommufd_device_unpreserve(struct liveupdate_session *s,
>> +			       struct iommufd_device *idev,
>> +			       u64 token)
>> +{
>> +	struct iommufd_group *igroup = idev->igroup;
>> +	struct iommufd_hwpt_paging *hwpt_paging;
>> +	struct iommufd_hw_pagetable *hwpt;
>> +	struct iommufd_attach *attach;
>> +
>> +	mutex_lock(&igroup->lock);
>> +	attach = xa_load(&igroup->pasid_attach, IOMMU_NO_PASID);
>> +	if (!attach) {
>> +		WARN_ON(-ENOENT);
>
>WARN_ON takes a condition.. if we want this to be printed always, why
>not WARN_ON(1, "...") ? What's the significance of having -ENOENT as a
>condition?

Will update this.
>
>> +		goto out;
>> +	}
>> +
>> +	hwpt = attach->hwpt;
>> +	hwpt_paging = find_hwpt_paging(hwpt);
>> +	if (!hwpt_paging || !hwpt_paging->lu_preserve) {
>> +		WARN_ON(-EINVAL);
>
>Same here for -EINVAL?

Same here.
>
>> +		goto out;
>> +	}
>> +
>> +	iommu_unpreserve_device(hwpt_paging->common.domain, idev->dev);
>> +out:
>> +	mutex_unlock(&igroup->lock);
>> +}
>> +EXPORT_SYMBOL_NS_GPL(iommufd_device_unpreserve, "IOMMUFD");
>> +#endif
>
>[ ----- >8 ----- ]
>
>Thanks,
>Praan

Thanks,
Sami