PCI passthru on Hyper-V (Part I)

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

Posted by Mukesh R 2 weeks, 4 days ago

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);
+
 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;
+	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);
+
+	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

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

Posted by Stanislav Kinsburskii 2 weeks, 4 days ago

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
>

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

Posted by Mukesh R 2 weeks, 1 day ago

On 1/20/26 14:22, Stanislav Kinsburskii wrote:
> 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?

Did you see the function implementation? It has other dependencies that
are later, it would need code reorg.

Thanks,
-Mukesh


>>   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.

Not really. It helps with debug by putting a quick print, and is
harmless.

>> +	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?

The ABI has device id defined as 64bits where this is assigned.

Thanks,
-Mukesh




> 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
>>

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

Posted by Manivannan Sadhasivam 1 week, 3 days ago

On Fri, Jan 23, 2026 at 04:42:54PM -0800, Mukesh R wrote:
> On 1/20/26 14:22, Stanislav Kinsburskii wrote:
> > 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?
> 
> Did you see the function implementation? It has other dependencies that
> are later, it would need code reorg.
> 
> Thanks,
> -Mukesh
> 
> 
> > >   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.
> 
> Not really. It helps with debug by putting a quick print, and is
> harmless.
> 

Such debug print do not exist now. So there is no need of a variable, drop it.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

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

Posted by Stanislav Kinsburskii 1 week, 5 days ago

On Fri, Jan 23, 2026 at 04:42:54PM -0800, Mukesh R wrote:
> On 1/20/26 14:22, Stanislav Kinsburskii wrote:
> > 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?
> 
> Did you see the function implementation? It has other dependencies that
> are later, it would need code reorg.
> 

Why not placing the caller side after the function definition then?

Thanks,
Stanislav

> Thanks,
> -Mukesh
> 
> 
> > >   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.
> 
> Not really. It helps with debug by putting a quick print, and is
> harmless.
> 
> > > +	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?
> 
> The ABI has device id defined as 64bits where this is assigned.
> 
> Thanks,
> -Mukesh
> 
> 
> 
> 
> > 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
> > >