The term “interrupt” brings to mind a signal that originates in the
hardware and which is handled in the kernel; even software interrupts are a
kernel concept. But there is, it seems, a use case for enabling user-space
processes to send interrupts directly to each other. An upcoming Intel
processor generation includes support for this capability; at the 2020 Linux Plumbers Conference,
Sohil Mehta ran a
Kernel-Summit session on how Linux might support that feature.