PCI: pciehp: Fix infinite loop in IRQ handler upon power fault

In the Linux kernel, the following vulnerability has been resolved:

PCI: pciehp: Fix infinite loop in IRQ handler upon power fault

The Power Fault Detected bit in the Slot Status register differs from

all other hotplug events in that it is sticky: It can only be cleared

after turning off slot power. Per PCIe r5.0, sec. 6.7.1.8:

If a power controller detects a main power fault on the hot-plug slot,

it must automatically set its internal main power fault latch [...].

The main power fault latch is cleared when software turns off power to

the hot-plug slot.

The stickiness used to cause interrupt storms and infinite loops which

were fixed in 2009 by commits 5651c48cfafe ("PCI pciehp: fix power fault

interrupt storm problem") and 99f0169c17f3 ("PCI: pciehp: enable

software notification on empty slots").

Unfortunately in 2020 the infinite loop issue was inadvertently

reintroduced by commit 8edf5332c393 ("PCI: pciehp: Fix MSI interrupt

race"): The hardirq handler pciehp_isr() clears the PFD bit until

pciehp's power_fault_detected flag is set. That happens in the IRQ

thread pciehp_ist(), which never learns of the event because the hardirq

handler is stuck in an infinite loop. Fix by setting the

power_fault_detected flag already in the hardirq handler.