From: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>

Running as nested root on MSHV imposes a different requirement
for the pci-hyperv controller.

In this setup, the interrupt will first come to the L1 (nested) hypervisor,
which will deliver it to the appropriate root CPU. Instead of issuing the
RETARGET hypercall, we should issue the MAP_DEVICE_INTERRUPT
hypercall to L1 to complete the setup.

Rename hv_arch_irq_unmask() to hv_irq_retarget_interrupt().

Co-developed-by: Jinank Jain <jinankjain@linux.microsoft.com>
Signed-off-by: Jinank Jain <jinankjain@linux.microsoft.com>
Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
---
 drivers/pci/controller/pci-hyperv.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 4d25754dfe2f..0f491c802fb9 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -600,7 +600,7 @@ static unsigned int hv_msi_get_int_vector(struct irq_data *data)
 #define hv_msi_prepare		pci_msi_prepare
 
 /**
- * hv_arch_irq_unmask() - "Unmask" the IRQ by setting its current
+ * hv_irq_retarget_interrupt() - "Unmask" the IRQ by setting its current
  * affinity.
  * @data:	Describes the IRQ
  *
@@ -609,7 +609,7 @@ static unsigned int hv_msi_get_int_vector(struct irq_data *data)
  * is built out of this PCI bus's instance GUID and the function
  * number of the device.
  */
-static void hv_arch_irq_unmask(struct irq_data *data)
+static void hv_irq_retarget_interrupt(struct irq_data *data)
 {
 	struct msi_desc *msi_desc = irq_data_get_msi_desc(data);
 	struct hv_retarget_device_interrupt *params;
@@ -714,6 +714,20 @@ static void hv_arch_irq_unmask(struct irq_data *data)
 		dev_err(&hbus->hdev->device,
 			"%s() failed: %#llx", __func__, res);
 }
+
+static void hv_arch_irq_unmask(struct irq_data *data)
+{
+	if (hv_nested && hv_root_partition())
+		/*
+		 * In case of the nested root partition, the nested hypervisor
+		 * is taking care of interrupt remapping and thus the
+		 * MAP_DEVICE_INTERRUPT hypercall is required instead of
+		 * RETARGET_INTERRUPT.
+		 */
+		(void)hv_map_msi_interrupt(data, NULL);
+	else
+		hv_irq_retarget_interrupt(data);
+}
 #elif defined(CONFIG_ARM64)
 /*
  * SPI vectors to use for vPCI; arch SPIs range is [32, 1019], but leaving a bit
-- 
2.34.1

On Tue, Jun 10, 2025 at 04:52:06PM -0700, Nuno Das Neves wrote:
> From: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> 
> Running as nested root on MSHV imposes a different requirement
> for the pci-hyperv controller.
> 
> In this setup, the interrupt will first come to the L1 (nested) hypervisor,
> which will deliver it to the appropriate root CPU. Instead of issuing the
> RETARGET hypercall, we should issue the MAP_DEVICE_INTERRUPT
> hypercall to L1 to complete the setup.

Maybe strengthen this to say that this issues MAP_DEVICE_INTERRUPT
instead of RETARGET in this case?  (Not just that we "should".) 

> Rename hv_arch_irq_unmask() to hv_irq_retarget_interrupt().

On 6/13/2025 12:36 PM, Bjorn Helgaas wrote:
> On Tue, Jun 10, 2025 at 04:52:06PM -0700, Nuno Das Neves wrote:
>> From: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
>>
>> Running as nested root on MSHV imposes a different requirement
>> for the pci-hyperv controller.
>>
>> In this setup, the interrupt will first come to the L1 (nested) hypervisor,
>> which will deliver it to the appropriate root CPU. Instead of issuing the
>> RETARGET hypercall, we should issue the MAP_DEVICE_INTERRUPT
>> hypercall to L1 to complete the setup.
> 
> Maybe strengthen this to say that this issues MAP_DEVICE_INTERRUPT
> instead of RETARGET in this case?  (Not just that we "should".) 
> 

Good suggestion, thanks.

>> Rename hv_arch_irq_unmask() to hv_irq_retarget_interrupt().