FAILED: patch "[PATCH] PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 86bdd16e8f390d51bae9e77a4bc4164ca2f580fe
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090342-washer-satchel-06ca@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 86bdd16e8f390d51bae9e77a4bc4164ca2f580fe Mon Sep 17 00:00:00 2001
From: Naman Jain <[email protected]>
Date: Mon, 10 Aug 2026 09:07:13 +0000
Subject: [PATCH] PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI
irqchip

The Hyper-V vPCI MSI irqchip never installs an irq_retrigger() callback.

On CPU hot-unplug fixup_irqs() migrates the interrupts which are affine to the outgoing CPU to a new target. If an interrupt still has its pending bit set in the outgoing CPU's IRR at that point, fixup_irqs() resends it on the new target through the irqchip's irq_retrigger() callback. As the Hyper-V PCI/MSI chip does not provide that callback, the pending interrupt is silently dropped, which can result in lost interrupts, stalls and "No irq handler for vector" messages during CPU hotplug.

Install irq_chip_retrigger_hierarchy() as the irq_retrigger() callback for the Hyper-V PCI/MSI irqchip, so that a pending interrupt is resent on its new target CPU via the parent x86 vector domain.

index cfc8fa403dad..89816a2bd7cd 100644
@@ -2119,6 +2119,7 @@ static bool hv_pcie_init_dev_msi_info(struct device *dev, struct irq_domain *dom
 	info->ops->msi_prepare = hv_msi_prepare;
 
 	chip->irq_set_affinity = irq_chip_set_affinity_parent;
+	chip->irq_retrigger = irq_chip_retrigger_hierarchy;
 
 	if (IS_ENABLED(CONFIG_X86))
 		chip->flags |= IRQCHIP_MOVE_DEFERRED;

The Hyper-V vPCI MSI irqchip never installs an irq_retrigger() callback.

On CPU hot-unplug fixup_irqs() migrates the interrupts which are affine to the outgoing CPU to a new target. If an interrupt still has its pending bit set in the outgoing CPU's IRR at that point, fixup_irqs() resends it on the new target through the irqchip's irq_retrigger() callback. As the Hyper-V PCI/MSI chip does not provide that callback, the pending interrupt is silently dropped, which can result in lost interrupts, stalls and "No irq handler for vector" messages during CPU hotplug.

Install irq_chip_retrigger_hierarchy() as the irq_retrigger() callback for the Hyper-V PCI/MSI irqchip, so that a pending interrupt is resent on its new target CPU via the parent x86 vector domain.

---
 drivers/pci/controller/pci-hyperv.c | 1 +
 1 file changed, 1 insertion(+)

index 58430ca37bbdf..4ff94e93a538f 100644
@@ -1978,6 +1978,7 @@ static struct irq_chip hv_msi_irq_chip = {
 	.name			= "Hyper-V PCIe MSI",
 	.irq_compose_msi_msg	= hv_compose_msi_msg,
 	.irq_set_affinity	= irq_chip_set_affinity_parent,
+	.irq_retrigger		= irq_chip_retrigger_hierarchy,
 #ifdef CONFIG_X86
 	.irq_ack		= irq_chip_ack_parent,
 #elif defined(CONFIG_ARM64)

2.43.0

Queued for 6.1, thanks.

Thanks,
Sasha