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

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

On 7/28/2026 7:34 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> 
> Pre-existing issues:
> - [High] The fix for dropped pending interrupts during CPU hot-unplug was missed in the sister Hyper-V root partition MSI domain.
> --
> 
> --- Patch [1]: [PATCH 1/3] PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI irqchip ---
> commit b8b1c843c457dd145f0d360b44f4b1bf34bd8cf5
> Author: Naman Jain <namjain@linux.microsoft.com>
> 
> 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. 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.
> 
> 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>
> 
>> 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;
> 
> [Severity: High]
> This isn't a bug introduced by this patch, but does the sister Hyper-V root
> partition MSI domain in arch/x86/hyperv/irqdomain.c also need this fix?
> 
> Looking at hv_init_dev_msi_info(), it appears to be missing the exact same
> callback initialization for the root partition's top-level irq_chip:
> 
> arch/x86/hyperv/irqdomain.c:hv_init_dev_msi_info() {
> 	...
> 	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;
> }
> 
> If a CPU is hot-unplugged while a device MSI interrupt is pending in its
> local APIC IRR, could fixup_irqs() fail to resend the pending interrupt
> to the new target CPU because this callback is NULL?
> 
> This could potentially lead to the same lost interrupts and I/O stalls
> described in this commit message, just in the root partition MSI domain
> instead of the guest paravirtual MSI domain.
> 
>>   
>>   	if (IS_ENABLED(CONFIG_X86))
>>   		chip->flags |= IRQCHIP_MOVE_DEFERRED;
>>
> 

I am not planning to include this in this series, since this issue is 
not seen in root partition yet and I am not sure if it is applicable 
here. Second patch would anyways fix it going forward, but I am OK 
adding the change for this, if we need.

Regards,
Naman