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

From: Yu Zhang <[email protected]> Sent: Tuesday, August 11, 2026 8:50 AM
> 
> From: Wei Liu <[email protected]>
> 
> 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
>