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

[Aditya Garg <gargaditya@linux.microsoft.com>]

On 28-07-2026 19:21, Naman Jain wrote:
> 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;

Reviewed-by: Aditya Garg <gargaditya@linux.microsoft.com>