Re: [PATCH v8 07/15] iommufd/viommu: Keep a reference to the KVM file

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

Hi Aneesh,

On Wed,  4 Nov 2026 21:46:24 +0530
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org> wrote:

> From: Nicolin Chen <nicolinc@nvidia.com>
> 
> The TSM vDevice operations need access to the KVM associated with the
> device's vIOMMU. Save the device's KVM file in the iommufd_viommu
> when the vIOMMU is allocated, and take a file reference so it remains
> valid for the lifetime of the vIOMMU.
> 
> Release the reference when the vIOMMU is destroyed.
> 
> Reject vdevice allocation when the device's KVM association differs
> from the vIOMMU's, including when only one has a KVM association.
> Allow allocation when both associations are NULL.
> 
> Based on an original patch by
> Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> 
> [nicolinc: hold kvm's users_count]
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> [aneesh.kumar: Switch to use kvm_file]
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  drivers/iommu/iommufd/viommu.c | 10 ++++++++++
>  include/linux/iommufd.h        |  1 +
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/iommu/iommufd/viommu.c
> b/drivers/iommu/iommufd/viommu.c index f7951057a1e5..0dbd382eeb98
> 100644 --- a/drivers/iommu/iommufd/viommu.c
> +++ b/drivers/iommu/iommufd/viommu.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0-only
>  /* Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES
>   */
> +#include <linux/file.h>
>  #include "iommufd_private.h"
>  
>  void iommufd_viommu_destroy(struct iommufd_object *obj)
> @@ -11,6 +12,8 @@ void iommufd_viommu_destroy(struct iommufd_object
> *obj) if (viommu->ops && viommu->ops->destroy)
>  		viommu->ops->destroy(viommu);
>  	refcount_dec(&viommu->hwpt->common.obj.users);
> +	if (viommu->kvm_file)
> +		fput(viommu->kvm_file);
>  	xa_destroy(&viommu->vdevs);
>  }
>  
> @@ -82,6 +85,8 @@ int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd
> *ucmd) }
>  
>  	xa_init(&viommu->vdevs);
> +	if (idev->kvm_file)
> +		viommu->kvm_file = get_file(idev->kvm_file);
>  	viommu->type = cmd->type;
>  	viommu->ictx = ucmd->ictx;
>  	viommu->hwpt = hwpt_paging;
> @@ -171,6 +176,11 @@ int iommufd_vdevice_alloc_ioctl(struct
> iommufd_ucmd *ucmd) goto out_put_viommu;
>  	}
>  
> +	if (idev->kvm_file != viommu->kvm_file) {
> +		rc = -EINVAL;
> +		goto out_put_idev;
> +	}
> +
>  	iommu_dev = iommufd_device_get_iommu_dev(idev);
>  	if (!iommu_dev || viommu->iommu_dev != iommu_dev) {
>  		rc = -EINVAL;
> diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
> index b03ce0187454..c15d80f611b9 100644
> --- a/include/linux/iommufd.h
> +++ b/include/linux/iommufd.h
> @@ -103,6 +103,7 @@ struct iommufd_viommu {
>  	struct iommufd_ctx *ictx;
>  	struct iommu_device *iommu_dev;
>  	struct iommufd_hwpt_paging *hwpt;
> +	struct file *kvm_file;
>  
>  	const struct iommufd_viommu_ops *ops;
>  
Reviewed-by: Jacob Pan <jacob.pan@linux.microsoft.com>

We may need to enable non-kvm file (such as mshv) eventually, but
until then this looks good to me.