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

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

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@linux.microsoft.com/
* 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@linux.microsoft.com/
* 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@linux.microsoft.com/#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

 arch/x86/kernel/apic/io_apic.c      |  2 --
 arch/x86/kernel/apic/msi.c          | 12 ++++++++----
 arch/x86/kernel/hpet.c              |  1 -
 arch/x86/kernel/irq.c               | 19 +++++++++++--------
 drivers/iommu/amd/init.c            |  1 -
 drivers/pci/controller/pci-hyperv.c |  1 -
 6 files changed, 19 insertions(+), 17 deletions(-)


base-commit: 944a035ecca915ae947905dcfb03f2b9dc6d032c
-- 
2.43.0