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

On Fri, Aug 14, 2026 at 03:31:08PM +0000, Michael Kelley wrote:
> 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.
> 

Thank you, Michael.
Indeed, there's no reason to treat this data structure differently.
Will drop the static_assert() and keep the explicit padding.

B.R.
Yu

> 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
> > 
>