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Re: [Xen-devel] [RFC v3 2/2] x86/xen: allow privcmd hypercalls to be preempted

On Thu, 22 Jan 2015 12:24:47 -0800
Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:

> > Also, please remove the "notrace", because function tracing goes an
> > extra step to not require RCU being visible. The only thing you get
> > with notrace is not being able to trace an otherwise traceable function.
> >
> Is this also true for kprobes?  And can kprobes nest inside function
> tracing hooks?

No, kprobes are a bit more fragile than function tracing or tracepoints.

And nothing should nest inside a function hook (except for interrupts,
they are fine).

> The other issue, above and beyond RCU, is that we can't let kprobes
> run on the int3 stack.  If Xen upcalls can happen when interrupts are
> off, then we may need this protection to prevent that type of
> recursion.  (This will be much less scary in 3.20, because userspace
> int3 instructions will no longer execute on the int3 stack.)

Does this execute between the start of the int3 interrupt handler and
the call of do_int3()?

-- Steve

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