On Apr 28, 2019, at 10:51 AM, Steven Rostedt rostedt@goodmis.org wrote:
On Sun, 28 Apr 2019 10:41:10 -0700 Andy Lutomirski luto@amacapital.net 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.