Re: [PATCH RFC 1/9] iommu: Introduce external attach domain type

[Mostafa Saleh <smostafa@google.com>]

On Fri, Sep 25, 2026 at 12:07:34PM -0700, Jacob Pan wrote:
> Add IOMMU_DOMAIN_EXTERNAL for externally managed domains that move or
> attach devices to another VM address space provisioned by an external
> owner, such as a type 1 hypervisor.
> 
> This is not a paging domain and is not sysfs-selectable as a default
> domain type. It requires external owner context, such as a vIOMMU.
> 

Can't we use a IOMMU_DOMAIN_BLOCKED domain for that, AFAIU, the host never
inserts any mapping?

Thanks,
Mostafa

> PV IOMMU drivers are expected to use it when moving a device to a guest
> VM with an already-created S2 IOPT.
> 
> Assisted-by: GPT-5.6 Sol
> Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>
> ---
>  drivers/iommu/iommu.c | 2 ++
>  include/linux/iommu.h | 9 +++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index cd1bca7ede9a..d0bd3ef00379 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -220,6 +220,8 @@ static const char *iommu_domain_type_str(unsigned int t)
>  		return "Translated";
>  	case IOMMU_DOMAIN_PLATFORM:
>  		return "Platform";
> +	case IOMMU_DOMAIN_EXTERNAL:
> +		return "External";
>  	default:
>  		return "Unknown";
>  	}
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index ac43b8b93f14..ede77b90f0fd 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -188,6 +188,7 @@ enum iommu_domain_cookie_type {
>  
>  #define __IOMMU_DOMAIN_NESTED	(1U << 6)  /* User-managed address space nested
>  					      on a stage-2 translation        */
> +#define __IOMMU_DOMAIN_EXTERNAL	(1U << 7)  /* Externally managed translation */
>  
>  #define IOMMU_DOMAIN_ALLOC_FLAGS ~__IOMMU_DOMAIN_DMA_FQ
>  /*
> @@ -207,6 +208,13 @@ enum iommu_domain_cookie_type {
>   *				  represented by mm_struct's.
>   *	IOMMU_DOMAIN_PLATFORM	- Legacy domain for drivers that do their own
>   *				  dma_api stuff. Do not use in new drivers.
> + *	IOMMU_DOMAIN_EXTERNAL	- Externally managed domain for moving/attaching
> + *				  devices to another VM address space
> + *				  provisioned by the external owner, such as
> + *				  a type 1 hypervisor. This is not a
> + *				  sysfs-selectable default domain type; it
> + *				  requires external owner context such as a
> + *				  vIOMMU.
>   */
>  #define IOMMU_DOMAIN_BLOCKED	(0U)
>  #define IOMMU_DOMAIN_IDENTITY	(__IOMMU_DOMAIN_PT)
> @@ -219,6 +227,7 @@ enum iommu_domain_cookie_type {
>  #define IOMMU_DOMAIN_SVA	(__IOMMU_DOMAIN_SVA)
>  #define IOMMU_DOMAIN_PLATFORM	(__IOMMU_DOMAIN_PLATFORM)
>  #define IOMMU_DOMAIN_NESTED	(__IOMMU_DOMAIN_NESTED)
> +#define IOMMU_DOMAIN_EXTERNAL	(__IOMMU_DOMAIN_EXTERNAL)
>  
>  struct iommu_domain {
>  	unsigned type;
> -- 
> 2.43.0
> 
>