Re: [Qemu-devel] [PATCH v8 0/5] hypertrace: Lightweight guest-to-QEMU trace channel

[Stefan Hajnoczi]

On Fri, Aug 25, 2017 at 08:34:54PM -0400, Emilio G. Cota wrote:
> On Sun, Jul 30, 2017 at 17:08:18 +0300, Lluís Vilanova wrote:
> > The hypertrace channel allows guest code to emit events in QEMU (the host) 
> > using
> > its tracing infrastructure (see "docs/trace.txt"). This works in both 
> > 'system'
> > and 'user' modes, is architecture-agnostic and introduces minimal noise on 
> > the
> > guest.
> > 
> > See first commit for a full description, use-cases and an example.
> > 
> > Signed-off-by: Lluís Vilanova <address@hidden>
> 
> This would be indeed very useful once TCG instrumentation is in place.
> 
> However, I'm not very excited about this being PCI-only and Linux-only for
> system mode
> I wonder how we could make this work on all hosts -- did you consider using
> "magic" instructions? We'd need a different magic instruction for each
> guest ISA, but the library would hide that anyway (and the library code
> would be the same for user and system modes).

Magic instructions can potentially be implemented more efficiently in
TCG too.  They wouldn't work under KVM/HAX/hvf accelerators though.

Stefan