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

[Sean Christopherson]

On Sat, Aug 28, 2021, Peter Zijlstra wrote:
> On Fri, Aug 27, 2021 at 05:35:45PM -0700, Sean Christopherson wrote:
> > Like Xu (2):
> >   perf/core: Rework guest callbacks to prepare for static_call support
> >   perf/core: Use static_call to optimize perf_guest_info_callbacks
> > 
> > Sean Christopherson (11):
> >   perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and
> >     deref
> >   KVM: x86: Register perf callbacks after calling vendor's
> >     hardware_setup()
> >   KVM: x86: Register Processor Trace interrupt hook iff PT enabled in
> >     guest
> >   perf: Stop pretending that perf can handle multiple guest callbacks
> >   perf: Force architectures to opt-in to guest callbacks
> >   KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu
> >     variable
> >   KVM: x86: More precisely identify NMI from guest when handling PMI
> >   KVM: Move x86's perf guest info callbacks to generic KVM
> >   KVM: x86: Move Intel Processor Trace interrupt handler to vmx.c
> >   KVM: arm64: Convert to the generic perf callbacks
> >   KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c /
> >     pmu.c

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

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?

> ---
> 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.