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Message-ID: <aXABVTS6xDb2GB2s@skinsburskii.localdomain>
Date: Tue, 20 Jan 2026 14:27:33 -0800
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: Mukesh R <mrathor@...ux.microsoft.com>
Cc: linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
linux-pci@...r.kernel.org, linux-arch@...r.kernel.org,
kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
decui@...rosoft.com, longli@...rosoft.com, catalin.marinas@....com,
will@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, hpa@...or.com, joro@...tes.org,
lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
robh@...nel.org, bhelgaas@...gle.com, arnd@...db.de,
nunodasneves@...ux.microsoft.com, mhklinux@...look.com,
romank@...ux.microsoft.com
Subject: Re: [PATCH v0 11/15] x86/hyperv: Build logical device ids for PCI
passthru hcalls
On Mon, Jan 19, 2026 at 10:42:26PM -0800, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@...ux.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@...ux.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
>
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