Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Thu, Sep 16, 2021 at 09:37:43PM +0000, Sean Christopherson wrote:
> On Sat, Aug 28, 2021, Peter Zijlstra wrote:

> Argh, sorry, I somehow managed to miss all of your replies.  I'll get back to
> this series next week.  Thanks for the quick response!
> 
> > Lets keep the whole intel_pt crud inside x86...
> 
> In theory, I like the idea of burying intel_pt inside x86 (and even in
> Intel+VMX code for the most part), but the actual implementation is a
> bit gross.  Because of the whole "KVM can be a module" thing,

ARGH!! we should really fix that. I've heard other archs have made much
better choices here.

> either
> the static call and __static_call_return0 would need to be exported,
> or a new register/unregister pair would have to be exported.

So I don't mind exporting __static_call_return0, but exporting a raw
static_call is much like exporting a function pointer :/

> The unregister path would also need its own synchronize_rcu().  In general, I
> don't love duplicating the logic, but it's not the end of the world.
> 
> Either way works for me.  Paolo or Peter, do either of you have a preference?

Can we de-feature kvm as a module and only have this PT functionality
when built-in? :-)


> > ---
> > Index: linux-2.6/arch/x86/events/core.c
> > ===================================================================
> > --- linux-2.6.orig/arch/x86/events/core.c
> > +++ linux-2.6/arch/x86/events/core.c
> > @@ -92,7 +92,7 @@ DEFINE_STATIC_CALL_RET0(x86_pmu_guest_ge
> >  
> >  DEFINE_STATIC_CALL_RET0(x86_guest_state, *(perf_guest_cbs->state));
> >  DEFINE_STATIC_CALL_RET0(x86_guest_get_ip, *(perf_guest_cbs->get_ip));
> > -DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, 
> > *(perf_guest_cbs->handle_intel_pt_intr));
> > +DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, unsigned int 
> > (*)(void));
> 
> FWIW, the param needs to be a raw function, not a function pointer. 

Yeah, I keep making that mistake.. and I wrote the bloody thing :/

I have a 'fix' for that, but I need to finish that and also flag-day
change :-(

  https://lkml.kernel.org/r/YS+0eIeAJsRRArk4@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx