x86/hotplug: Silence APIC only after all interrupts are migrated

There is a race when taking a CPU offline. Current code looks like this:

native_cpu_disable()
{
	...
	apic_soft_disable();
	/*
	 * Any existing set bits for pending interrupt to
	 * this CPU are preserved and will be sent via IPI
	 * to another CPU by fixup_irqs().
	 */
	cpu_disable_common();
	{
		....
		/*
		 * Race window happens here. Once local APIC has been
		 * disabled any new interrupts from the device to
		 * the old CPU are lost
		 */
		fixup_irqs(); // Too late to capture anything in IRR.
		...
	}
}

The fix is to disable the APIC *after* cpu_disable_common().

Testing was done with a USB NIC that provided a source of frequent
interrupts. A script migrated interrupts to a specific CPU and
then took that CPU offline.

Fixes: 60dcaad5736f ("x86/hotplug: Silence APIC and NMI when CPU is dead")
Reported-by: Evan Green <[email protected]>
Signed-off-by: Ashok Raj <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Mathias Nyman <[email protected]>
Tested-by: Evan Green <[email protected]>
Reviewed-by: Evan Green <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/lkml/[email protected]/
Link: https://lore.kernel.org/r/[email protected]

0 files changed, 0 insertions, 0 deletions