[RFC PATCH v6 04/11] iommufd/viommu: Keep a reference to the KVM file

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

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.

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]
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 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 4081deda9b33..bf5d58d55939 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);
 }
 
@@ -76,6 +79,8 @@ 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;
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;
 
-- 
2.43.0