Re: [PATCH v0 10/15] PCI: hv: Build device id for a VMBus device

Stanislav Kinsburskii
2026-01-20T22:22:36Z

On Mon, Jan 19, 2026 at 10:42:25PM -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. This device id refers
> to that specific device during the lifetime of passthru.
>
> An L1VH VM only contains VMBus based devices. A device id for a VMBus
> device is slightly different in that it uses the hv_pcibus_device info
> for building it to make sure it matches exactly what the hypervisor
> expects. This VMBus based device id is needed when attaching devices in
> an L1VH based guest VM. Before building it, a check is done to make sure
> the device is a valid VMBus device.
>
> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
> ---
> arch/x86/include/asm/mshyperv.h | 2 ++
> drivers/pci/controller/pci-hyperv.c | 29 +++++++++++++++++++++++++++++
> 2 files changed, 31 insertions(+)
>
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index eef4c3a5ba28..0d7fdfb25e76 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -188,6 +188,8 @@ bool hv_vcpu_is_preempted(int vcpu);
> static inline void hv_apic_init(void) {}
> #endif
>
> +u64 hv_pci_vmbus_device_id(struct pci_dev *pdev);
> +
> struct irq_domain *hv_create_pci_msi_domain(void);
>
> int hv_map_msi_interrupt(struct irq_data *data,
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 8bc6a38c9b5a..40f0b06bb966 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -579,6 +579,8 @@ static void hv_pci_onchannelcallback(void *context);
> #define DELIVERY_MODE APIC_DELIVERY_MODE_FIXED
> #define HV_MSI_CHIP_FLAGS MSI_CHIP_FLAG_SET_ACK
>
> +static bool hv_vmbus_pci_device(struct pci_bus *pbus);
> +

Why not moving this static function definition above the called instead of
defining the prototype?

> static int hv_pci_irqchip_init(void)
> {
> return 0;
> @@ -598,6 +600,26 @@ static unsigned int hv_msi_get_int_vector(struct irq_data *data)
>
> #define hv_msi_prepare pci_msi_prepare
>
> +u64 hv_pci_vmbus_device_id(struct pci_dev *pdev)
> +{
> + u64 u64val;

This variable is redundant.

> + struct hv_pcibus_device *hbus;
> + struct pci_bus *pbus = pdev->bus;
> +
> + if (!hv_vmbus_pci_device(pbus))
> + return 0;
> +
> + hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
> + u64val = (hbus->hdev->dev_instance.b[5] << 24) |
> + (hbus->hdev->dev_instance.b[4] << 16) |
> + (hbus->hdev->dev_instance.b[7] << 8) |
> + (hbus->hdev->dev_instance.b[6] & 0xf8) |
> + PCI_FUNC(pdev->devfn);
> +

It looks like this value always fits into 32 bit, so what is the value
in returning 64 bit?

Thanks,
Stanislav

> + return u64val;
> +}
> +EXPORT_SYMBOL_GPL(hv_pci_vmbus_device_id);
> +
> /**
> * hv_irq_retarget_interrupt() - "Unmask" the IRQ by setting its current
> * affinity.
> @@ -1404,6 +1426,13 @@ static struct pci_ops hv_pcifront_ops = {
> .write = hv_pcifront_write_config,
> };
>
> +#ifdef CONFIG_X86
> +static bool hv_vmbus_pci_device(struct pci_bus *pbus)
> +{
> + return pbus->ops == &hv_pcifront_ops;
> +}
> +#endif /* CONFIG_X86 */
> +
> /*
> * Paravirtual backchannel
> *
> --
> 2.51.2.vfs.0.1
>