Re: [RFC PATCH 2/3] iommufd/viommu: Add support to associate viommu with kvm instance

[Jason Gunthorpe <jgg@nvidia.com>]

> +static int viommu_get_kvm(struct iommufd_viommu *viommu, int kvm_vm_fd)
> +{
> +	int rc = -EBADF;
> +	struct kvm *kvm;
> +	struct fd f = fdget(kvm_vm_fd);
> +
> +	if (!fd_file(f) || !file_is_kvm(fd_file(f)))
> +		goto err_out;
> +
> +	kvm = fd_file(f)->private_data;
> +	if (!kvm)
> +		goto err_out;

Is this actually possible? Doesn't it suggest that the file refcount is
not sufficient? If not possible then remove it.

> +
> +	/* hold the kvm reference via file descriptor */
> +	viommu->kvm_fd = f;

You can't store a 'struct fd', fdget is a special "fast" function that only
works within system calls. You must use the normal fget flow here.

> diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
> index f29b6c44655e..b3b962d857c7 100644
> --- a/include/uapi/linux/iommufd.h
> +++ b/include/uapi/linux/iommufd.h
> @@ -957,6 +957,7 @@ enum iommu_viommu_type {
>  	IOMMU_VIOMMU_TYPE_ARM_SMMUV3 = 1,
>  };
>  
> +#define IOMMU_VIOMMU_KVM_FD	BIT(0)

Needs a kdoc

Jason