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

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Jacob Pan <jacob.pan@linux.microsoft.com> writes:

> Hi Aneesh,
>
> On Thu,  8 Oct 2026 11:29:47 +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.
>> 
>> 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: jgg@ziepe.ca
>> Cc: kevin.tian@intel.com
>> Cc: joro@8bytes.org
>> Cc: will@kernel.org
>> Cc: robin.murphy@arm.com
>> 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 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?
>

Agreed. I will add the below.

modified    drivers/iommu/iommufd/viommu.c
@@ -212,6 +212,11 @@ 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;
+	}
+
 	if (viommu->iommu_dev) {
 		iommu_dev = iommufd_device_get_iommu_dev(idev);
 		if (!iommu_dev || viommu->iommu_dev != iommu_dev) {



-aneesh