linux-kernel - Re: [RFC PATCH v1 07/38] iommufd/viommu: Add support to associate viommu with kvm instance

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Message-ID: <20250729172621.00006344@huawei.com>
Date: Tue, 29 Jul 2025 17:26:21 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
CC: <linux-coco@...ts.linux.dev>, <kvmarm@...ts.linux.dev>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <aik@....com>,
	<lukas@...ner.de>, Samuel Ortiz <sameo@...osinc.com>, Xu Yilun
	<yilun.xu@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>, "Suzuki K
 Poulose" <Suzuki.Poulose@....com>, Steven Price <steven.price@....com>,
	Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
	Will Deacon <will@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>
Subject: Re: [RFC PATCH v1 07/38] iommufd/viommu: Add support to associate
 viommu with kvm instance

On Mon, 28 Jul 2025 19:21:44 +0530
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org> wrote:

> The associated kvm instance will be used in later patch by iommufd to
> bind a tdi to kvm.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@...nel.org>
> ---
>  drivers/iommu/iommufd/viommu.c | 45 +++++++++++++++++++++++++++++++++-
>  include/linux/iommufd.h        |  3 +++
>  include/uapi/linux/iommufd.h   | 12 +++++++++
>  3 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommufd/viommu.c b/drivers/iommu/iommufd/viommu.c
> index 2ca5809b238b..59f1e1176f7f 100644
> --- a/drivers/iommu/iommufd/viommu.c
> +++ b/drivers/iommu/iommufd/viommu.c
> @@ -2,6 +2,36 @@
>  /* Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES
>   */
>  #include "iommufd_private.h"
> +#include "linux/tsm.h"
> +
> +#if IS_ENABLED(CONFIG_KVM)
> +#include <linux/kvm_host.h>
> +
> +static int viommu_get_kvm(struct iommufd_viommu *viommu, int kvm_vm_fd)
> +{
> +	int rc = -EBADF;
> +	struct file *filp;
> +
> +	filp = fget(kvm_vm_fd);
> +
> +	if (!file_is_kvm(filp))
> +		goto err_out;
> +
> +	/* hold the kvm reference via file descriptor */
> +	viommu->kvm_filp = filp;
> +	return 0;
> +err_out:
> +	viommu->kvm_filp = NULL;

Is this to undo side effects from this function on error?

kvm_filp is only set after all error paths so maybe this isn't
needed?

If this isn't needed then use __free(fput) and no_free_ptr() to
deal with filp more simply and in teh erorr path can just return -EBADF
directly rather than the goto.

Or are we avoiding that stuff in iommufd?

> +	fput(filp);
> +	return rc;
> +}
> +
> +static void viommu_put_kvm(struct iommufd_viommu *viommu)
> +{
> +	fput(viommu->kvm_filp);
> +	viommu->kvm_filp = NULL;
> +}
> +#endif