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

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Date:   Fri, 17 Sep 2021 09:28:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>, Guo Ren <guoren@...nel.org>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-csky@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Artem Kashkanov <artem.kashkanov@...el.com>,
        Like Xu <like.xu.linux@...il.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Subject: Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks

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@hirez.programming.kicks-ass.net