I also think there is another issue here. When an IRQ is taken from SIE, will
user_mode(regs) always be false, or could it be true if the guest userspace is
running? If it can be true I think tha context tracking checks can complain,
and it*might* be possible to trigger a panic().
In irqentry_enter(), if user_mode(regs) == true, we call
irqentry_enter_from_user_mode -> __enter_from_user_mode(). There we check that
the context is CONTEXT_USER, but IIUC that will be CONTEXT_GUEST at this point.
We also call arch_check_user_regs(), and IIUC this might permit a malicious
guest to trigger a host panic by way of debug_user_asce(), but I may have
misunderstood and that might not be possible.