Re: [PATCH v7 08/16] iommufd/viommu: Keep a reference to the KVM file

[Jacob Pan]

Hi Aneesh,

On Thu,  8 Oct 2026 11:29:47 +0530
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@xxxxxxxxxx> wrote:

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> 
> 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.
> 
> Based on an original patch by
> Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
> 
> [nicolinc: hold kvm's users_count]
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> [aneesh.kumar: Switch to use kvm_file]
> Cc: jgg@xxxxxxxx
> Cc: kevin.tian@xxxxxxxxx
> Cc: joro@xxxxxxxxxx
> Cc: will@xxxxxxxxxx
> Cc: robin.murphy@xxxxxxx
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@xxxxxxxxxx>
> ---
>  drivers/iommu/iommufd/viommu.c | 5 +++++
>  include/linux/iommufd.h        | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/iommu/iommufd/viommu.c
> b/drivers/iommu/iommufd/viommu.c index f7951057a1e5..b7489ed259bd
> 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);
So kvm_file will persist inside viommu even when no more vdevice exists
under the viommu. In that case, don't we need to check idev->kvm_file
matches viommu->kvm_file during vdevice allocation?

Otherwise, it appears possible to associate a device belonging to a
different KVM VM with the existing vIOMMU, no?

>  	viommu->type = cmd->type;
>  	viommu->ictx = ucmd->ictx;
>  	viommu->hwpt = hwpt_paging;
> diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
> index 0a0bb4abfbd2..3267717f676d 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;
>