Re: [PATCH v4 0/4] x86/irq: Fix lost interrupts on CPU hot-unplug

[Wei Liu]

On Wed, Sep 09, 2026 at 06:44:44AM +0000, Naman Jain wrote:
> On CPU hot-unplug, fixup_irqs() re-injects interrupts that are still
> pending in the outgoing CPU's IRR via the irqchip's irq_retrigger()
> callback. The Hyper-V root partition PCI/MSI irqchip lost that callback
> when it was converted to msi_create_parent_irq_domain(), so such a
> pending interrupt is silently dropped, leading to lost interrupts, stalls
> and "No irq handler for vector" messages.
> 
> Patch 1 is the minimal, backportable fix (Fixes:/Cc: stable) that restores
> irq_chip_retrigger_hierarchy() on the Hyper-V root partition PCI/MSI chip.
> The equivalent guest pci-hyperv.c fix from the previous version is already
> merged, so it is dropped here.
> 
> Patch 2 then switches fixup_irqs() to have a fallback call to
> irq_chip_retrigger_hierarchy() directly, if a chip does not define
> irq_retrigger callback.
> 
> Patch 3 makes a similar change in msi_set_affinity()
> 
> Patch 4 then drops the now-redundant irq_retrigger() initializations.
> This way, patch 2-4 do not need to be backported.
> 
> Changes since v3:
> https://lore.kernel.org/all/20260907065129.269262-1-namjain@xxxxxxxxxxxxxxxxxxx/
> * Move irq_retrigger setting to hv_init_dev_msi_info() in patch 1
>   (Michael, Nam) 
> * Add if-else fallback check in msi_set_affinity() in patch 3 (Michael)
> * Break patch 3 into two separate patches, while *keeping review tags*.
> 
> Changes since v2:
> https://lore.kernel.org/all/20260810090716.2325295-1-namjain@xxxxxxxxxxxxxxxxxxx/
> * Add a backportable fix for Hyper-V root partition irqchip (Wei)
> * Add a check for custom irq_retrigger implementations and add direct
>   irq_chip_retrigger_hierarchy() calls as a fallback if it is not
>   defined by a chip. (Sashiko, Michael)
> * Removed local loop variable change, and continue using the irq_desc
>   accessor function (Michael)
> * Did not pick "Acked-by: Manivannan Sadhasivam" as it was on v1, and v3
>   is a functionally different to some extent, specially patch 2.
>   Requesting you to please review again.
> 
> Changes since v1:
> https://lore.kernel.org/all/20260728135117.2888175-1-namjain@xxxxxxxxxxxxxxxxxxx/#t
> * Added Review tags
> * Adding minor clarification in commit msg of patch 2 (Shradha)
> 
> Original RFC: https://lore.kernel.org/all/87y0f3jhd6.ffs@fw13/
> 
> Naman Jain (4):
>   x86/hyperv: Set irq_retrigger for root partition PCI/MSI irqchip
>   x86/irq: Fall back to irq_chip_retrigger_hierarchy() in fixup_irqs()
>   x86/irq: Fall back to irq_chip_retrigger_hierarchy() in
>     msi_set_affinity()
>   x86/irq, iommu/amd, x86/hyperv, PCI: Drop redundant irq_retrigger
>     inits
> 

I checked linux-next next-20260911. This series has not been applied.

This patch series needs to be applied in one go, since patch 4 depends
on patch 1.

I'm fine with carrying this through the hyperv-fixes tree, or let it go
through the x86 tree. Just let me know.

Thanks,
Wei