[PATCH v2 0/3] x86/irq: Fix lost interrupts on CPU hot-unplug for Hyper-V PCI/MSI

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 vPCI MSI irqchip never installs one, 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 installs
irq_chip_retrigger_hierarchy() on the Hyper-V PCI/MSI chip. Patch 2 then
switches fixup_irqs() to call irq_chip_retrigger_hierarchy() directly, so
the retrigger works for any stacked irqchip without a per-chip callback.
Patch 3 drops the now-redundant irq_retrigger() initializations.
This way, patch 2 and 3 do not need to be backported.

Changes since v1:
https://lore.kernel.org/all/20260728135117.2888175-1-namjain@linux.microsoft.com/#t (local)
* Added Review tags
* Adding minor clarification in commit msg of patch 2 (Shradha)

Original RFC: https://lore.kernel.org/all/87y0f3jhd6.ffs@fw13/ (local)

Naman Jain (3):
  PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI irqchip
  x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs()
  x86/irq, iommu/amd, PCI: Drop redundant irq_retrigger inits

 arch/x86/kernel/apic/io_apic.c |  2 --
 arch/x86/kernel/apic/msi.c     |  4 +---
 arch/x86/kernel/hpet.c         |  1 -
 arch/x86/kernel/irq.c          | 23 +++++++----------------
 drivers/iommu/amd/init.c       |  1 -
 5 files changed, 8 insertions(+), 23 deletions(-)

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2.43.0