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

[Jacob Pan <jacob.pan@linux.microsoft.com>]

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.

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