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

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Date:   Thu, 16 Sep 2021 21:37:43 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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.