[PATCH v3 0/1] x86/hyperv: MSI parent domain conversion

[PATCH v3 0/1] x86/hyperv: MSI parent domain conversion

[Nam Cao]

The initial implementation of PCI/MSI interrupt domains in the hierarchical
interrupt domain model used a shortcut by providing a global PCI/MSI
domain.

This works because the PCI/MSI[X] hardware is standardized and uniform, but
it violates the basic design principle of hierarchical interrupt domains:
Each hardware block involved in the interrupt delivery chain should have a
separate interrupt domain.

For PCI/MSI[X], the interrupt controller is per PCI device and not a global
made-up entity.

Unsurprisingly, the shortcut turned out to have downsides as it does not
allow dynamic allocation of interrupt vectors after initialization and it
prevents supporting IMS on PCI. For further details, see:

https://lore.kernel.org/lkml/20221111120501.026511281@linutronix.de/

The solution is implementing per device MSI domains, this means the
entities which provide global PCI/MSI domain so far have to implement MSI
parent domain functionality instead.

This series converts the x86 hyperv driver to implement MSI parent domain.

Changes in v3:

  - Drop the merged patch

  - Rebase onto hyperv-fixes

 arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
 drivers/hv/Kconfig          |   1 +
 2 files changed, 77 insertions(+), 35 deletions(-)

-- 
2.49.0

[PATCH v3 1/1] x86/hyperv: Switch to msi_create_parent_irq_domain()

[Nam Cao]

Move away from the legacy MSI domain setup, switch to use
msi_create_parent_irq_domain().

While doing the conversion, I noticed that hv_irq_compose_msi_msg() is
doing more than it is supposed to (composing message content). The
interrupt allocation bits should be moved into hv_msi_domain_alloc().
However, I have no hardware to test this change, therefore I leave a TODO
note.

Signed-off-by: Nam Cao <namcao@linutronix.de>
---
 arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
 drivers/hv/Kconfig          |   1 +
 2 files changed, 77 insertions(+), 35 deletions(-)

diff --git a/arch/x86/hyperv/irqdomain.c b/arch/x86/hyperv/irqdomain.c
index 090f5ac9f492..c3ba12b1bc07 100644
--- a/arch/x86/hyperv/irqdomain.c
+++ b/arch/x86/hyperv/irqdomain.c
@@ -11,6 +11,7 @@
 #include <linux/pci.h>
 #include <linux/irq.h>
 #include <linux/export.h>
+#include <linux/irqchip/irq-msi-lib.h>
 #include <asm/mshyperv.h>
 
 static int hv_map_interrupt(union hv_device_id device_id, bool level,
@@ -289,59 +290,99 @@ static void hv_teardown_msi_irq(struct pci_dev *dev, struct irq_data *irqd)
 	(void)hv_unmap_msi_interrupt(dev, &old_entry);
 }
 
-static void hv_msi_free_irq(struct irq_domain *domain,
-			    struct msi_domain_info *info, unsigned int virq)
-{
-	struct irq_data *irqd = irq_get_irq_data(virq);
-	struct msi_desc *desc;
-
-	if (!irqd)
-		return;
-
-	desc = irq_data_get_msi_desc(irqd);
-	if (!desc || !desc->irq || WARN_ON_ONCE(!dev_is_pci(desc->dev)))
-		return;
-
-	hv_teardown_msi_irq(to_pci_dev(desc->dev), irqd);
-}
-
 /*
  * IRQ Chip for MSI PCI/PCI-X/PCI-Express Devices,
  * which implement the MSI or MSI-X Capability Structure.
  */
 static struct irq_chip hv_pci_msi_controller = {
 	.name			= "HV-PCI-MSI",
-	.irq_unmask		= pci_msi_unmask_irq,
-	.irq_mask		= pci_msi_mask_irq,
 	.irq_ack		= irq_chip_ack_parent,
-	.irq_retrigger		= irq_chip_retrigger_hierarchy,
 	.irq_compose_msi_msg	= hv_irq_compose_msi_msg,
-	.irq_set_affinity	= msi_domain_set_affinity,
-	.flags			= IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED,
+	.irq_set_affinity	= irq_chip_set_affinity_parent,
 };
 
-static struct msi_domain_ops pci_msi_domain_ops = {
-	.msi_free		= hv_msi_free_irq,
-	.msi_prepare		= pci_msi_prepare,
+static bool hv_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
+				 struct irq_domain *real_parent, struct msi_domain_info *info)
+{
+	struct irq_chip *chip = info->chip;
+
+	if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
+		return false;
+
+	chip->flags |= IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED;
+
+	info->ops->msi_prepare = pci_msi_prepare;
+
+	return true;
+}
+
+#define HV_MSI_FLAGS_SUPPORTED	(MSI_GENERIC_FLAGS_MASK | MSI_FLAG_PCI_MSIX)
+#define HV_MSI_FLAGS_REQUIRED	(MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS)
+
+static struct msi_parent_ops hv_msi_parent_ops = {
+	.supported_flags	= HV_MSI_FLAGS_SUPPORTED,
+	.required_flags		= HV_MSI_FLAGS_REQUIRED,
+	.bus_select_token	= DOMAIN_BUS_NEXUS,
+	.bus_select_mask	= MATCH_PCI_MSI,
+	.chip_flags		= MSI_CHIP_FLAG_SET_ACK,
+	.prefix			= "HV-",
+	.init_dev_msi_info	= hv_init_dev_msi_info,
 };
 
-static struct msi_domain_info hv_pci_msi_domain_info = {
-	.flags		= MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
-			  MSI_FLAG_PCI_MSIX,
-	.ops		= &pci_msi_domain_ops,
-	.chip		= &hv_pci_msi_controller,
-	.handler	= handle_edge_irq,
-	.handler_name	= "edge",
+static int hv_msi_domain_alloc(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs,
+			       void *arg)
+{
+	/*
+	 * TODO: The allocation bits of hv_irq_compose_msi_msg(), i.e. everything except
+	 * entry_to_msi_msg() should be in here.
+	 */
+
+	int ret;
+
+	ret = irq_domain_alloc_irqs_parent(d, virq, nr_irqs, arg);
+	if (ret)
+		return ret;
+
+	for (int i = 0; i < nr_irqs; ++i) {
+		irq_domain_set_info(d, virq + i, 0, &hv_pci_msi_controller, NULL,
+				    handle_edge_irq, NULL, "edge");
+	}
+	return 0;
+}
+
+static void hv_msi_domain_free(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs)
+{
+	for (int i = 0; i < nr_irqs; ++i) {
+		struct irq_data *irqd = irq_domain_get_irq_data(d, virq);
+		struct msi_desc *desc;
+
+		desc = irq_data_get_msi_desc(irqd);
+		if (!desc || !desc->irq || WARN_ON_ONCE(!dev_is_pci(desc->dev)))
+			continue;
+
+		hv_teardown_msi_irq(to_pci_dev(desc->dev), irqd);
+	}
+	irq_domain_free_irqs_top(d, virq, nr_irqs);
+}
+
+static const struct irq_domain_ops hv_msi_domain_ops = {
+	.select	= msi_lib_irq_domain_select,
+	.alloc	= hv_msi_domain_alloc,
+	.free	= hv_msi_domain_free,
 };
 
 struct irq_domain * __init hv_create_pci_msi_domain(void)
 {
 	struct irq_domain *d = NULL;
-	struct fwnode_handle *fn;
 
-	fn = irq_domain_alloc_named_fwnode("HV-PCI-MSI");
-	if (fn)
-		d = pci_msi_create_irq_domain(fn, &hv_pci_msi_domain_info, x86_vector_domain);
+	struct irq_domain_info info = {
+		.fwnode		= irq_domain_alloc_named_fwnode("HV-PCI-MSI"),
+		.ops		= &hv_msi_domain_ops,
+		.parent		= x86_vector_domain,
+	};
+
+	if (info.fwnode)
+		d = msi_create_parent_irq_domain(&info, &hv_msi_parent_ops);
 
 	/* No point in going further if we can't get an irq domain */
 	BUG_ON(!d);
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 57623ca7f350..9afffedce290 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -10,6 +10,7 @@ config HYPERV
 	select X86_HV_CALLBACK_VECTOR if X86
 	select OF_EARLY_FLATTREE if OF
 	select SYSFB if EFI && !HYPERV_VTL_MODE
+	select IRQ_MSI_LIB if X86
 	help
 	  Select this option to run Linux as a Hyper-V client operating
 	  system.
-- 
2.49.0

Re: [PATCH v3 0/1] x86/hyperv: MSI parent domain conversion

[Wei Liu]

Nuno, can you please take a look at this patch?

On Fri, Jul 18, 2025 at 09:57:49PM +0200, Nam Cao wrote:
> The initial implementation of PCI/MSI interrupt domains in the hierarchical
> interrupt domain model used a shortcut by providing a global PCI/MSI
> domain.
> 
> This works because the PCI/MSI[X] hardware is standardized and uniform, but
> it violates the basic design principle of hierarchical interrupt domains:
> Each hardware block involved in the interrupt delivery chain should have a
> separate interrupt domain.
> 
> For PCI/MSI[X], the interrupt controller is per PCI device and not a global
> made-up entity.
> 
> Unsurprisingly, the shortcut turned out to have downsides as it does not
> allow dynamic allocation of interrupt vectors after initialization and it
> prevents supporting IMS on PCI. For further details, see:
> 
> https://lore.kernel.org/lkml/20221111120501.026511281@linutronix.de/
> 
> The solution is implementing per device MSI domains, this means the
> entities which provide global PCI/MSI domain so far have to implement MSI
> parent domain functionality instead.
> 
> This series converts the x86 hyperv driver to implement MSI parent domain.
> 
> Changes in v3:
> 
>   - Drop the merged patch
> 
>   - Rebase onto hyperv-fixes
> 
>  arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
>  drivers/hv/Kconfig          |   1 +
>  2 files changed, 77 insertions(+), 35 deletions(-)
> 
> -- 
> 2.49.0
> 

Re: [PATCH v3 1/1] x86/hyperv: Switch to msi_create_parent_irq_domain()

[Shradha Gupta]

On Fri, Jul 18, 2025 at 09:57:50PM +0200, Nam Cao wrote:
> Move away from the legacy MSI domain setup, switch to use
> msi_create_parent_irq_domain().
> 
> While doing the conversion, I noticed that hv_irq_compose_msi_msg() is
> doing more than it is supposed to (composing message content). The
> interrupt allocation bits should be moved into hv_msi_domain_alloc().
> However, I have no hardware to test this change, therefore I leave a TODO
> note.

Hi Nam,

JFYI, I am working on a patch to optimize the hv_irq_compose_msi_msg()
callback to prevent potential busy looping due to 
PCI_CREATE_INTERRUPT_MESSAGE hypercall. I think I can handle this TODO
in that patch

Thanks,
Shradha
> 
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> ---
>  arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
>  drivers/hv/Kconfig          |   1 +
>  2 files changed, 77 insertions(+), 35 deletions(-)
> 
> diff --git a/arch/x86/hyperv/irqdomain.c b/arch/x86/hyperv/irqdomain.c
> index 090f5ac9f492..c3ba12b1bc07 100644
> --- a/arch/x86/hyperv/irqdomain.c
> +++ b/arch/x86/hyperv/irqdomain.c
> @@ -11,6 +11,7 @@
>  #include <linux/pci.h>
>  #include <linux/irq.h>
>  #include <linux/export.h>
> +#include <linux/irqchip/irq-msi-lib.h>
>  #include <asm/mshyperv.h>
>  
>  static int hv_map_interrupt(union hv_device_id device_id, bool level,
> @@ -289,59 +290,99 @@ static void hv_teardown_msi_irq(struct pci_dev *dev, struct irq_data *irqd)
>  	(void)hv_unmap_msi_interrupt(dev, &old_entry);
>  }
>  
> -static void hv_msi_free_irq(struct irq_domain *domain,
> -			    struct msi_domain_info *info, unsigned int virq)
> -{
> -	struct irq_data *irqd = irq_get_irq_data(virq);
> -	struct msi_desc *desc;
> -
> -	if (!irqd)
> -		return;
> -
> -	desc = irq_data_get_msi_desc(irqd);
> -	if (!desc || !desc->irq || WARN_ON_ONCE(!dev_is_pci(desc->dev)))
> -		return;
> -
> -	hv_teardown_msi_irq(to_pci_dev(desc->dev), irqd);
> -}
> -
>  /*
>   * IRQ Chip for MSI PCI/PCI-X/PCI-Express Devices,
>   * which implement the MSI or MSI-X Capability Structure.
>   */
>  static struct irq_chip hv_pci_msi_controller = {
>  	.name			= "HV-PCI-MSI",
> -	.irq_unmask		= pci_msi_unmask_irq,
> -	.irq_mask		= pci_msi_mask_irq,
>  	.irq_ack		= irq_chip_ack_parent,
> -	.irq_retrigger		= irq_chip_retrigger_hierarchy,
>  	.irq_compose_msi_msg	= hv_irq_compose_msi_msg,
> -	.irq_set_affinity	= msi_domain_set_affinity,
> -	.flags			= IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED,
> +	.irq_set_affinity	= irq_chip_set_affinity_parent,
>  };
>  
> -static struct msi_domain_ops pci_msi_domain_ops = {
> -	.msi_free		= hv_msi_free_irq,
> -	.msi_prepare		= pci_msi_prepare,
> +static bool hv_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
> +				 struct irq_domain *real_parent, struct msi_domain_info *info)
> +{
> +	struct irq_chip *chip = info->chip;
> +
> +	if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
> +		return false;
> +
> +	chip->flags |= IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED;
> +
> +	info->ops->msi_prepare = pci_msi_prepare;
> +
> +	return true;
> +}
> +
> +#define HV_MSI_FLAGS_SUPPORTED	(MSI_GENERIC_FLAGS_MASK | MSI_FLAG_PCI_MSIX)
> +#define HV_MSI_FLAGS_REQUIRED	(MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS)
> +
> +static struct msi_parent_ops hv_msi_parent_ops = {
> +	.supported_flags	= HV_MSI_FLAGS_SUPPORTED,
> +	.required_flags		= HV_MSI_FLAGS_REQUIRED,
> +	.bus_select_token	= DOMAIN_BUS_NEXUS,
> +	.bus_select_mask	= MATCH_PCI_MSI,
> +	.chip_flags		= MSI_CHIP_FLAG_SET_ACK,
> +	.prefix			= "HV-",
> +	.init_dev_msi_info	= hv_init_dev_msi_info,
>  };
>  
> -static struct msi_domain_info hv_pci_msi_domain_info = {
> -	.flags		= MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
> -			  MSI_FLAG_PCI_MSIX,
> -	.ops		= &pci_msi_domain_ops,
> -	.chip		= &hv_pci_msi_controller,
> -	.handler	= handle_edge_irq,
> -	.handler_name	= "edge",
> +static int hv_msi_domain_alloc(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs,
> +			       void *arg)
> +{
> +	/*
> +	 * TODO: The allocation bits of hv_irq_compose_msi_msg(), i.e. everything except
> +	 * entry_to_msi_msg() should be in here.
> +	 */
> +
> +	int ret;
> +
> +	ret = irq_domain_alloc_irqs_parent(d, virq, nr_irqs, arg);
> +	if (ret)
> +		return ret;
> +
> +	for (int i = 0; i < nr_irqs; ++i) {
> +		irq_domain_set_info(d, virq + i, 0, &hv_pci_msi_controller, NULL,
> +				    handle_edge_irq, NULL, "edge");
> +	}
> +	return 0;
> +}
> +
> +static void hv_msi_domain_free(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs)
> +{
> +	for (int i = 0; i < nr_irqs; ++i) {
> +		struct irq_data *irqd = irq_domain_get_irq_data(d, virq);
> +		struct msi_desc *desc;
> +
> +		desc = irq_data_get_msi_desc(irqd);
> +		if (!desc || !desc->irq || WARN_ON_ONCE(!dev_is_pci(desc->dev)))
> +			continue;
> +
> +		hv_teardown_msi_irq(to_pci_dev(desc->dev), irqd);
> +	}
> +	irq_domain_free_irqs_top(d, virq, nr_irqs);
> +}
> +
> +static const struct irq_domain_ops hv_msi_domain_ops = {
> +	.select	= msi_lib_irq_domain_select,
> +	.alloc	= hv_msi_domain_alloc,
> +	.free	= hv_msi_domain_free,
>  };
>  
>  struct irq_domain * __init hv_create_pci_msi_domain(void)
>  {
>  	struct irq_domain *d = NULL;
> -	struct fwnode_handle *fn;
>  
> -	fn = irq_domain_alloc_named_fwnode("HV-PCI-MSI");
> -	if (fn)
> -		d = pci_msi_create_irq_domain(fn, &hv_pci_msi_domain_info, x86_vector_domain);
> +	struct irq_domain_info info = {
> +		.fwnode		= irq_domain_alloc_named_fwnode("HV-PCI-MSI"),
> +		.ops		= &hv_msi_domain_ops,
> +		.parent		= x86_vector_domain,
> +	};
> +
> +	if (info.fwnode)
> +		d = msi_create_parent_irq_domain(&info, &hv_msi_parent_ops);
>  
>  	/* No point in going further if we can't get an irq domain */
>  	BUG_ON(!d);
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 57623ca7f350..9afffedce290 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -10,6 +10,7 @@ config HYPERV
>  	select X86_HV_CALLBACK_VECTOR if X86
>  	select OF_EARLY_FLATTREE if OF
>  	select SYSFB if EFI && !HYPERV_VTL_MODE
> +	select IRQ_MSI_LIB if X86
>  	help
>  	  Select this option to run Linux as a Hyper-V client operating
>  	  system.
> -- 
> 2.49.0
> 

Re: [PATCH v3 0/1] x86/hyperv: MSI parent domain conversion

[Thomas Gleixner]

On Thu, Jul 24 2025 at 16:47, Wei Liu wrote:
> Nuno, can you please take a look at this patch?

Can we get this moving so that the legacy PCI stuff can be retired?

Thanks,

        tglx

Re: [PATCH v3 1/1] x86/hyperv: Switch to msi_create_parent_irq_domain()

[Nuno Das Neves]

On 7/18/2025 12:57 PM, Nam Cao wrote:
> Move away from the legacy MSI domain setup, switch to use
> msi_create_parent_irq_domain().
> 
> While doing the conversion, I noticed that hv_irq_compose_msi_msg() is
> doing more than it is supposed to (composing message content). The
> interrupt allocation bits should be moved into hv_msi_domain_alloc().
> However, I have no hardware to test this change, therefore I leave a TODO
> note.
> 
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> ---
>  arch/x86/hyperv/irqdomain.c | 111 ++++++++++++++++++++++++------------
>  drivers/hv/Kconfig          |   1 +
>  2 files changed, 77 insertions(+), 35 deletions(-)

Tested on nested root partition.

Looks good, thanks.

Tested-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>