[PATCH 1/3] PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI irqchip

[Naman Jain <namjain@linux.microsoft.com>]

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.

Fixes: 4daace0d8ce85 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Cc: stable@vger.kernel.org
Suggested-by: Long Li <longli@microsoft.com>
Suggested-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
---
 drivers/pci/controller/pci-hyperv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index cfc8fa403dad6..89816a2bd7cd3 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -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;
-- 
2.43.0