Re: [PATCH v4 1/4] x86/hyperv: Set irq_retrigger for root partition PCI/MSI irqchip

[Nam Cao <namcao@linutronix.de>]

Naman Jain <namjain@linux.microsoft.com> writes:

> The Hyper-V root partition vPCI MSI irqchip lost its irq_retrigger()
> callback when it was converted to msi_create_parent_irq_domain(). The
> callback was present on the original irqchip and was dropped during that
> conversion.
>
> On CPU hot-unplug fixup_irqs() migrates the interrupts which are affine to
> the outgoing CPU to a new target. If an interrupt still has its pending bit
> set in the outgoing CPU's IRR at that point, fixup_irqs() resends it on the
> new target through the irqchip's irq_retrigger() callback. As the root
> partition PCI/MSI chip no longer provides that callback, the pending
> interrupt is silently dropped, which can result in lost interrupts, stalls
> and "No irq handler for vector" messages during CPU hotplug.
>
> Restore irq_chip_retrigger_hierarchy() as the irq_retrigger() callback for
> the root partition PCI/MSI irqchip, so that a pending interrupt is resent
> on its new target CPU via the parent x86 vector domain.
>
> Fixes: 4691db0704ac ("x86/hyperv: Switch to msi_create_parent_irq_domain()")
> Cc: stable@vger.kernel.org
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>

Reviewed-by: Nam Cao <namcao@linutronix.de>