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

From: Sean Christopherson <seanjc@google.com>
To: Peter Zijlstra <peterz@infradead.org>
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: Thu, 16 Sep 2021 21:37:43 +0000	[thread overview]
Message-ID: <YUO5J/jTMa2KGbsq@google.com> (raw)
In-Reply-To: <20210828201336.GD4353@worktop.programming.kicks-ass.net>

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. 