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

[Naman Jain]

On 7/28/2026 7:34 PM, sashiko-...@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 <namj...@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: sta...@vger.kernel.org
Suggested-by: Long Li <lon...@microsoft.com>
Suggested-by: Thomas Gleixner <t...@kernel.org>
Signed-off-by: Naman Jain <namj...@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