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

Pranjal Shrivastava
2026-03-25T20:24:34Z

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?

> + 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?

> + 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?

> + 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