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

[sashiko-bot@kernel.org]

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.
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--- 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;
>

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Sashiko AI review · https://sashiko.dev/#/patchset/20260728135117.2888175-1-namjain@linux.microsoft.com?part=1