Re: [PATCH v0 11/15] x86/hyperv: Build logical device ids for PCI passthru hcalls

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

On Mon, Jan 19, 2026 at 10:42:26PM -0800, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@linux.microsoft.com>
> 
> On Hyper-V, most hypercalls related to PCI passthru to map/unmap regions,
> interrupts, etc need a device id as a parameter. A device id refers
> to a specific device. A device id is of two types:
>    o Logical: used for direct attach (see below) hypercalls. A logical
>               device id is a unique 62bit value that is created and
>               sent during the initial device attach. Then all further
>               communications (for interrupt remaps etc) must use this
>               logical id.
>    o PCI: used for device domain hypercalls such as map, unmap, etc.
>           This is built using actual device BDF info.
> 
>    PS: Since an L1VH only supports direct attaches, a logical device id
>        on an L1VH VM is always a VMBus device id. For non-L1VH cases,
>        we just use PCI BDF info, altho not strictly needed, to build the
>        logical device id.
> 
> At a high level, Hyper-V supports two ways to do PCI passthru:
>   1. Device Domain: root must create a device domain in the hypervisor,
>      and do map/unmap hypercalls for mapping and unmapping guest RAM.
>      All hypervisor communications use device id of type PCI for
>      identifying and referencing the device.
> 
>   2. Direct Attach: the hypervisor will simply use the guest's HW
>      page table for mappings, thus the host need not do map/unmap
>      hypercalls. A direct attached device must be referenced
>      via logical device id and never via the PCI device id. For an
>      L1VH root/parent, Hyper-V only supports direct attaches.
> 
> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
> ---
>  arch/x86/hyperv/irqdomain.c     | 60 ++++++++++++++++++++++++++++++---
>  arch/x86/include/asm/mshyperv.h | 14 ++++++++
>  2 files changed, 70 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/hyperv/irqdomain.c b/arch/x86/hyperv/irqdomain.c
> index ccbe5848a28f..33017aa0caa4 100644
> --- a/arch/x86/hyperv/irqdomain.c
> +++ b/arch/x86/hyperv/irqdomain.c
> @@ -137,7 +137,7 @@ static int get_rid_cb(struct pci_dev *pdev, u16 alias, void *data)
>  	return 0;
>  }
>  
> -static union hv_device_id hv_build_devid_type_pci(struct pci_dev *pdev)
> +static u64 hv_build_devid_type_pci(struct pci_dev *pdev)
>  {
>  	int pos;
>  	union hv_device_id hv_devid;
> @@ -197,7 +197,58 @@ static union hv_device_id hv_build_devid_type_pci(struct pci_dev *pdev)
>  	}
>  
>  out:
> -	return hv_devid;
> +	return hv_devid.as_uint64;
> +}
> +
> +/* Build device id for direct attached devices */
> +static u64 hv_build_devid_type_logical(struct pci_dev *pdev)
> +{
> +	hv_pci_segment segment;
> +	union hv_device_id hv_devid;
> +	union hv_pci_bdf bdf = {.as_uint16 = 0};
> +	struct rid_data data = {
> +		.bridge = NULL,
> +		.rid = PCI_DEVID(pdev->bus->number, pdev->devfn)
> +	};
> +
> +	segment = pci_domain_nr(pdev->bus);
> +	bdf.bus = PCI_BUS_NUM(data.rid);
> +	bdf.device = PCI_SLOT(data.rid);
> +	bdf.function = PCI_FUNC(data.rid);
> +
> +	hv_devid.as_uint64 = 0;
> +	hv_devid.device_type = HV_DEVICE_TYPE_LOGICAL;
> +	hv_devid.logical.id = (u64)segment << 16 | bdf.as_uint16;
> +
> +	return hv_devid.as_uint64;
> +}
> +
> +/* Build device id after the device has been attached */
> +u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type type)
> +{
> +	if (type == HV_DEVICE_TYPE_LOGICAL) {
> +		if (hv_l1vh_partition())
> +			return hv_pci_vmbus_device_id(pdev);

Should this one be renamed into hv_build_devid_type_vmbus() to align
with the other two function names?

Thanks,
Stanislav

> +		else
> +			return hv_build_devid_type_logical(pdev);
> +	} else if (type == HV_DEVICE_TYPE_PCI)
> +		return hv_build_devid_type_pci(pdev);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(hv_build_devid_oftype);
> +
> +/* Build device id for the interrupt path */
> +static u64 hv_build_irq_devid(struct pci_dev *pdev)
> +{
> +	enum hv_device_type dev_type;
> +
> +	if (hv_pcidev_is_attached_dev(pdev) || hv_l1vh_partition())
> +		dev_type = HV_DEVICE_TYPE_LOGICAL;
> +	else
> +		dev_type = HV_DEVICE_TYPE_PCI;
> +
> +	return hv_build_devid_oftype(pdev, dev_type);
>  }
>  
>  /*
> @@ -221,7 +272,7 @@ int hv_map_msi_interrupt(struct irq_data *data,
>  
>  	msidesc = irq_data_get_msi_desc(data);
>  	pdev = msi_desc_to_pci_dev(msidesc);
> -	hv_devid = hv_build_devid_type_pci(pdev);
> +	hv_devid.as_uint64 = hv_build_irq_devid(pdev);
>  	cpu = cpumask_first(irq_data_get_effective_affinity_mask(data));
>  
>  	return hv_map_interrupt(hv_current_partition_id, hv_devid, false, cpu,
> @@ -296,7 +347,8 @@ static int hv_unmap_msi_interrupt(struct pci_dev *pdev,
>  {
>  	union hv_device_id hv_devid;
>  
> -	hv_devid = hv_build_devid_type_pci(pdev);
> +	hv_devid.as_uint64 = hv_build_irq_devid(pdev);
> +
>  	return hv_unmap_interrupt(hv_devid.as_uint64, irq_entry);
>  }
>  
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 0d7fdfb25e76..97477c5a8487 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -188,6 +188,20 @@ bool hv_vcpu_is_preempted(int vcpu);
>  static inline void hv_apic_init(void) {}
>  #endif
>  
> +#if IS_ENABLED(CONFIG_HYPERV_IOMMU)
> +static inline bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
> +{ return false; }       /* temporary */
> +u64 hv_build_devid_oftype(struct pci_dev *pdev, enum hv_device_type type);
> +#else	/* CONFIG_HYPERV_IOMMU */
> +static inline bool hv_pcidev_is_attached_dev(struct pci_dev *pdev)
> +{ return false; }
> +
> +static inline u64 hv_build_devid_oftype(struct pci_dev *pdev,
> +				       enum hv_device_type type)
> +{ return 0; }
> +
> +#endif	/* CONFIG_HYPERV_IOMMU */
> +
>  u64 hv_pci_vmbus_device_id(struct pci_dev *pdev);
>  
>  struct irq_domain *hv_create_pci_msi_domain(void);
> -- 
> 2.51.2.vfs.0.1
>