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Date:   Mon, 14 Mar 2022 16:50:33 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Matthew Rosato <mjrosato@linux.ibm.com>
Cc:     linux-s390@vger.kernel.org, cohuck@redhat.com,
        schnelle@linux.ibm.com, farman@linux.ibm.com, pmorel@linux.ibm.com,
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        pasic@linux.ibm.com, joro@8bytes.org, will@kernel.org,
        pbonzini@redhat.com, corbet@lwn.net, jgg@nvidia.com,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH v4 15/32] vfio: introduce KVM-owned IOMMU type
Message-ID: <20220314165033.6d2291a5.alex.williamson@redhat.com>
In-Reply-To: <20220314194451.58266-16-mjrosato@linux.ibm.com>
References: <20220314194451.58266-1-mjrosato@linux.ibm.com>
        <20220314194451.58266-16-mjrosato@linux.ibm.com>
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On Mon, 14 Mar 2022 15:44:34 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> s390x will introduce a new IOMMU domain type where the mappings are
> managed by KVM rather than in response to userspace mapping ioctls.  Allow
> for specifying this type on the VFIO_SET_IOMMU ioctl and triggering the
> appropriate iommu interface for overriding the default domain.
> 
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 12 +++++++++++-
>  include/uapi/linux/vfio.h       |  6 ++++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 9394aa9444c1..0bec97077d61 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -77,6 +77,7 @@ struct vfio_iommu {
>  	bool			nesting;
>  	bool			dirty_page_tracking;
>  	bool			container_open;
> +	bool			kvm;
>  	struct list_head	emulated_iommu_groups;
>  };
>  
> @@ -2203,7 +2204,12 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>  		goto out_free_group;
>  
>  	ret = -EIO;
> -	domain->domain = iommu_domain_alloc(bus);
> +
> +	if (iommu->kvm)
> +		domain->domain = iommu_domain_alloc_type(bus, IOMMU_DOMAIN_KVM);
> +	else
> +		domain->domain = iommu_domain_alloc(bus);
> +
>  	if (!domain->domain)
>  		goto out_free_domain;
>  
> @@ -2552,6 +2558,9 @@ static void *vfio_iommu_type1_open(unsigned long arg)
>  	case VFIO_TYPE1v2_IOMMU:
>  		iommu->v2 = true;
>  		break;
> +	case VFIO_KVM_IOMMU:
> +		iommu->kvm = true;
> +		break;
>  	default:
>  		kfree(iommu);
>  		return ERR_PTR(-EINVAL);
> @@ -2637,6 +2646,7 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
>  	case VFIO_TYPE1_NESTING_IOMMU:
>  	case VFIO_UNMAP_ALL:
>  	case VFIO_UPDATE_VADDR:
> +	case VFIO_KVM_IOMMU:
>  		return 1;
>  	case VFIO_DMA_CC_IOMMU:
>  		if (!iommu)
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index ef33ea002b0b..666edb6957ac 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -52,6 +52,12 @@
>  /* Supports the vaddr flag for DMA map and unmap */
>  #define VFIO_UPDATE_VADDR		10
>  
> +/*
> + * The KVM_IOMMU type implies that the hypervisor will control the mappings
> + * rather than userspace
> + */
> +#define VFIO_KVM_IOMMU			11

Then why is this hosted in the type1 code that exposes a wide variety
of userspace interfaces?  Thanks,

Alex