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

From: Peter Zijlstra <peterz@infradead.org>
To: Sean Christopherson <seanjc@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>, Guo Ren <guoren@kernel.org>,
	Nick Hu <nickhu@andestech.com>, Greentime Hu <green.hu@gmail.com>,
	Vincent Chen <deanbo422@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org,
	linux-riscv@lists.infradead.org, kvm@vger.kernel.org,
	xen-devel@lists.xenproject.org,
	Artem Kashkanov <artem.kashkanov@intel.com>,
	Like Xu <like.xu.linux@gmail.com>,
	Zhu Lingshan <lingshan.zhu@intel.com>
Subject: Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks
Date: Fri, 17 Sep 2021 09:28:41 +0200	[thread overview]
Message-ID: <YURDqVZ1UXKCiKPV@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YUO5J/jTMa2KGbsq@google.com>

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