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Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer


Ingo Molnar wrote:
ok, the structure and concept looks quite good now, really nice!

I'm wondering about something i suggested many moons ago: to look into the KVM decoder+emulator (arch/x86/kvm/x86_emulate.c).

I remember there were some issues with that (one problem being that the KVM decoder is a special-purpose thing covering specific range of execution environments - not a near-full integer-ops decoder like the one we are aiming for here) - are there any other fundamental problems beyond 'it has to be done' ?

Conceptually we want just a single piece of decoder logic in arch/x86/. If the KVM folks are cool with it we could factor out the KVM one into arch/x86/lib/. But ... if there are compelling reasons to leave the KVM one alone in its limited environment we can do that too.

kvm has three requirements not needed by kprobes:
- it wants to execute instructions, not just decode them, including generating faults where appropriate
- it is performance critical
- it needs to support 16-bit, 32-bit, and 64-bit instructions simultaneously


If an arch/x86/ decoder/emulator gives me these I'll gladly switch to it. x86_emulate.c is high on my list of most disliked code.

--
I have a truly marvellous patch that fixes the bug which this
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