linux-kernel - Re: [tip: perf/core] perf: Use EXPORT_SYMBOL_FOR

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Message-ID: <20251218083346.GG3708021@noisy.programming.kicks-ass.net>
Date: Thu, 18 Dec 2025 09:33:46 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: linux-kernel@...r.kernel.org, seanjc@...gle.com, sfr@...b.auug.org.au
Cc: linux-tip-commits@...r.kernel.org, x86@...nel.org, pbonzini@...hat.com,
	kvm@...r.kernel.org
Subject: Re: [tip: perf/core] perf: Use EXPORT_SYMBOL_FOR_KVM() for the
 mediated APIs

On Thu, Dec 18, 2025 at 09:31:09AM +0100, Peter Zijlstra wrote:
> On Wed, Dec 17, 2025 at 12:37:57PM -0000, tip-bot2 for Peter Zijlstra wrote:
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index e6a4b1e..376fb07 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -57,6 +57,7 @@
> >  #include <linux/task_work.h>
> >  #include <linux/percpu-rwsem.h>
> >  #include <linux/unwind_deferred.h>
> > +#include <linux/kvm_types.h>
> >  
> >  #include "internal.h"
> >  
> > @@ -6388,7 +6389,7 @@ int perf_create_mediated_pmu(void)
> >  	atomic_inc(&nr_mediated_pmu_vms);
> >  	return 0;
> >  }
> > -EXPORT_SYMBOL_GPL(perf_create_mediated_pmu);
> > +EXPORT_SYMBOL_FOR_KVM(perf_create_mediated_pmu);
> >  
> >  void perf_release_mediated_pmu(void)
> >  {
> > @@ -6397,7 +6398,7 @@ void perf_release_mediated_pmu(void)
> >  
> >  	atomic_dec(&nr_mediated_pmu_vms);
> >  }
> > -EXPORT_SYMBOL_GPL(perf_release_mediated_pmu);
> > +EXPORT_SYMBOL_FOR_KVM(perf_release_mediated_pmu);
> >  
> >  /* When loading a guest's mediated PMU, schedule out all exclude_guest events. */
> >  void perf_load_guest_context(void)
> 
> Bah, so the !KVM architectures hate on this.
> 
> Sean, would something like this be acceptable?

Hmm, the other option is doing something like so:

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 376fb07d869b..014d832e8eaa 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -57,7 +57,6 @@
 #include <linux/task_work.h>
 #include <linux/percpu-rwsem.h>
 #include <linux/unwind_deferred.h>
-#include <linux/kvm_types.h>
 
 #include "internal.h"
 
@@ -6325,6 +6324,8 @@ u64 perf_event_pause(struct perf_event *event, bool reset)
 EXPORT_SYMBOL_GPL(perf_event_pause);
 
 #ifdef CONFIG_PERF_GUEST_MEDIATED_PMU
+#include <linux/kvm_types.h>
+
 static atomic_t nr_include_guest_events __read_mostly;
 
 static atomic_t nr_mediated_pmu_vms __read_mostly;

> ---
> Subject: kvm: Fix linux/kvm_types.h for !KVM architectures
> 
> As is, <linux/kvm_types.h> hard relies on architectures having
> <asm/kvm_types.h> which (obviously) breaks for architectures that don't
> have KVM support.
> 
> This means generic code (kernel/events/ in this case) cannot use
> EXPORT_SYMBOL_FOR_KVM().
> 
> Rearrange things just so that <linux/kvm_types.h> becomes usable and
> provides the (expected) empty stub for EXPORT_SYMBOL_FOR_KVM() for !KVM.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index a568d8e6f4e8..a4cc13e41eec 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -6,6 +6,8 @@
>  #include <linux/bits.h>
>  #include <linux/export.h>
>  #include <linux/types.h>
> +
> +#ifdef CONFIG_KVM
>  #include <asm/kvm_types.h>
>  
>  #ifdef KVM_SUB_MODULES
> @@ -20,13 +22,14 @@
>   * if there are no submodules, e.g. to allow suppressing exports if KVM=m, but
>   * kvm.ko won't actually be built (due to lack of at least one submodule).
>   */
> -#ifndef EXPORT_SYMBOL_FOR_KVM
> -#if IS_MODULE(CONFIG_KVM)
> +#if defined(EXPORT_SYMBOL_FOR_KVM) && IS_MODULE(CONFIG_KVM)
>  #define EXPORT_SYMBOL_FOR_KVM(symbol) EXPORT_SYMBOL_FOR_MODULES(symbol, "kvm")
> -#else
> -#define EXPORT_SYMBOL_FOR_KVM(symbol)
>  #endif /* IS_MODULE(CONFIG_KVM) */
> -#endif /* EXPORT_SYMBOL_FOR_KVM */
> +#endif /* KVM_SUB_MODULES */
> +#endif
> +
> +#ifndef EXPORT_SYMBOL_FOR_KVM
> +#define EXPORTEXPORT_SYMBOL_FOR_KVM(symbol)
>  #endif
>  
>  #ifndef __ASSEMBLER__