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

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Message-ID: <20250728141026.GB26511@ziepe.ca>
Date: Mon, 28 Jul 2025 11:10:26 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
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>,
	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, Jul 28, 2025 at 07:21:44PM +0530, Aneesh Kumar K.V (Arm) wrote:

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

Missing stub functions for !CONFIG_KVM?

Looks like an OK design otherwise

> @@ -1057,6 +1068,7 @@ struct iommu_viommu_alloc {
>  	__u32 data_len;
>  	__u32 __reserved;
>  	__aligned_u64 data_uptr;
> +	__u32 kvm_vm_fd;

fds are __s32, they are signed numbers.

Jason