RE: [PATCH v3 1/5] hyperv: Introduce new hypercall interfaces used by Hyper-V guest IOMMU

From: Yu Zhang <redacted> Sent: Tuesday, August 11, 2026 8:50 AM

From: Wei Liu <wei.liu@kernel.org>

Hyper-V guest IOMMU is a para-virtualized IOMMU based on hypercalls.
Introduce the hypercalls used by the child partition to interact with
this facility.

These hypercalls fall into below categories:
- Detection and capability: HVCALL_GET_IOMMU_CAPABILITIES is used to
  detect the existence and capabilities of the guest IOMMU.

- Device management: HVCALL_GET_LOGICAL_DEVICE_PROPERTY is used to
  check whether an endpoint device is managed by the guest IOMMU.

- Domain management: A set of hypercalls is provided to handle the
  creation, configuration, and deletion of guest domains, as well as
  the attachment/detachment of endpoint devices to/from those domains.

- IOTLB flushing: HVCALL_FLUSH_DEVICE_DOMAIN is used to ask Hyper-V
  for a domain-selective IOTLB flush (which in its handler may flush
  the device TLB as well).

[snip]

+
+struct hv_input_device_domain {
+	u64 partition_id;
+	union hv_input_vtl owner_vtl;
+	u8 padding[7];
+	union hv_device_domain_id domain_id;
+} __packed;
+
+union hv_create_device_domain_flags {
+	u32 as_uint32;
+	struct {
+		u32 forward_progress_required: 1;
+		u32 inherit_owning_vtl: 1;
+		u32 reserved: 30;
+	} __packed;
+};
+
+struct hv_input_create_device_domain {
+	struct hv_input_device_domain device_domain;
+	union hv_create_device_domain_flags create_device_domain_flags;
+	u32 padding;
+} __packed;
+static_assert(sizeof(struct hv_input_create_device_domain) == 32);

The static_assert() here is unusual. For all the other hypercall
inputs/outputs where we rely on the structure definition to
be correct and the __packed to prevent the compiler from
adding/changing anything. If there's a reason for this one to be
different, a comment would help. If there's not really a reason,
I'd suggest dropping the static_assert() as superfluous.

Michael

+
+struct hv_input_delete_device_domain {
+	struct hv_input_device_domain device_domain;
+} __packed;
+
+struct hv_input_attach_device_domain {
+	struct hv_input_device_domain device_domain;
+	union hv_device_id device_id;
+} __packed;
+
+struct hv_input_detach_device_domain {
+	u64 partition_id;
+	union hv_device_id device_id;
+} __packed;
+
+struct hv_device_domain_settings {
+	struct {
+		/*
+		 * Enable translations. If not enabled, all transaction bypass
+		 * S1 translations.
+		 */
+		u64 translation_enabled: 1;
+		u64 blocked: 1;
+		/*
+		 * First stage address translation paging mode:
+		 * 0: 4-level paging (default)
+		 * 1: 5-level paging
+		 */
+		u64 first_stage_paging_mode: 1;
+		u64 reserved: 61;
+	} flags;
+
+	/* Address of translation table */
+	u64 page_table_root;
+} __packed;
+
+struct hv_input_configure_device_domain {
+	struct hv_input_device_domain device_domain;
+	struct hv_device_domain_settings settings;
+} __packed;
+
+struct hv_input_get_iommu_capabilities {
+	u64 partition_id;
+	u64 reserved;
+} __packed;
+
+struct hv_output_get_iommu_capabilities {
+	u32 size;
+	u16 reserved;
+	u8  max_iova_width;
+	u8  max_pasid_width;
+
+#define HV_IOMMU_CAP_PRESENT    BIT_ULL(0)
+#define HV_IOMMU_CAP_S2         BIT_ULL(1)
+#define HV_IOMMU_CAP_S1         BIT_ULL(2)
+#define HV_IOMMU_CAP_S1_5LVL    BIT_ULL(3)
+#define HV_IOMMU_CAP_PASID      BIT_ULL(4)
+#define HV_IOMMU_CAP_ATS        BIT_ULL(5)
+#define HV_IOMMU_CAP_PRI        BIT_ULL(6)
+
+	u64 iommu_cap;
+	u64 pgsize_bitmap;
+} __packed;
+
+enum hv_logical_device_property_code {
+	HV_LOGICAL_DEVICE_PROPERTY_PVIOMMU = 10,
+};
+
+struct hv_input_get_logical_device_property {
+	u64 partition_id;
+	u64 logical_device_id;
+	/* Takes values from enum hv_logical_device_property_code. */
+	u32 code;
+	u32 reserved;
+} __packed;
+
+struct hv_output_get_logical_device_property {
+#define HV_DEVICE_IOMMU_ENABLED	BIT_ULL(0)
+	u64 device_iommu;
+	u64 reserved;
+} __packed;
+
+struct hv_input_flush_device_domain {
+	struct hv_input_device_domain device_domain;
+	u32 flags;
+	u32 reserved;
+} __packed;
+
 #endif /* _HV_HVHDK_MINI_H */
--
2.52.0