> On Apr 28, 2019, at 10:51 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Sun, 28 Apr 2019 10:41:10 -0700 > Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > >>> Note that at any given point >>> in time, there can be at most four such call insn emulations pending: >>> namely at most one per "process", "irq", "softirq" and "nmi" context. >>> >> >> That’s quite an assumption. I think your list should also contain >> exception, exceptions nested inside that exception, and machine >> check, at the very least. I’m also wondering why irq and softirq are >> treated separately. > > 4 has usually been the context count we choose. But I guess in theory, > if we get exceptions then I could potentially be more. > > As for irq vs softirq, an interrupt can preempt a softirq. Interrupts > are enabled while softirqs are running. When sofirqs run, softirqs are > disabled to prevent nested softirqs. But interrupts are enabled again, > and another interrupt may come in while a softirq is executing. > >> >> All this makes me think that one of the other solutions we came up >> with last time we discussed this might be better. > > +100 > > Perhaps adding another slot into pt_regs that gets used by int3 to > store a slot to emulate a call on return? > > That’s not totally nuts, although finding pt_regs isn’t entirely trivial. I still think I prefer an approach where we just emulate the call directly.
