Re: [PATCH v3 08/16] perf: Force architectures to opt-in to guest callbacks

[Paolo Bonzini <pbonzini@redhat.com>]

On 22/09/21 02:05, Sean Christopherson wrote:
> Introduce GUEST_PERF_EVENTS and require architectures to select it to
> allow registering and using guest callbacks in perf.  This will hopefully
> make it more difficult for new architectures to add useless "support" for
> guest callbacks, e.g. via copy+paste.
> 
> Stubbing out the helpers has the happy bonus of avoiding a load of
> perf_guest_cbs when GUEST_PERF_EVENTS=n on arm64/x86.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/arm64/kvm/Kconfig     | 1 +
>   arch/x86/kvm/Kconfig       | 1 +
>   arch/x86/xen/Kconfig       | 1 +
>   include/linux/perf_event.h | 6 ++++++
>   init/Kconfig               | 4 ++++
>   kernel/events/core.c       | 2 ++
>   6 files changed, 15 insertions(+)
> 
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index a4eba0908bfa..f2121404c7c6 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -37,6 +37,7 @@ menuconfig KVM
>   	select HAVE_KVM_IRQ_BYPASS
>   	select HAVE_KVM_VCPU_RUN_PID_CHANGE
>   	select SCHED_INFO
> +	select GUEST_PERF_EVENTS if PERF_EVENTS
>   	help
>   	  Support hosting virtualized guest machines.
>   
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index ac69894eab88..699bf786fbce 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -36,6 +36,7 @@ config KVM
>   	select KVM_MMIO
>   	select SCHED_INFO
>   	select PERF_EVENTS
> +	select GUEST_PERF_EVENTS
>   	select HAVE_KVM_MSI
>   	select HAVE_KVM_CPU_RELAX_INTERCEPT
>   	select HAVE_KVM_NO_POLL
> diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
> index afc1da68b06d..d07595a9552d 100644
> --- a/arch/x86/xen/Kconfig
> +++ b/arch/x86/xen/Kconfig
> @@ -23,6 +23,7 @@ config XEN_PV
>   	select PARAVIRT_XXL
>   	select XEN_HAVE_PVMMU
>   	select XEN_HAVE_VPMU
> +	select GUEST_PERF_EVENTS
>   	help
>   	  Support running as a Xen PV guest.
>   
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index c0a6eaf55fb1..eefa197d5354 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1238,6 +1238,7 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
>   				 enum perf_bpf_event_type type,
>   				 u16 flags);
>   
> +#ifdef CONFIG_GUEST_PERF_EVENTS
>   extern struct perf_guest_info_callbacks *perf_guest_cbs;
>   static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
>   {
> @@ -1273,6 +1274,11 @@ static inline unsigned int perf_guest_handle_intel_pt_intr(void)
>   }
>   extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
>   extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
> +#else
> +static inline unsigned int perf_guest_state(void)		 { return 0; }
> +static inline unsigned long perf_guest_get_ip(void)		 { return 0; }
> +static inline unsigned int perf_guest_handle_intel_pt_intr(void) { return 0; }
> +#endif /* CONFIG_GUEST_PERF_EVENTS */

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Having perf_guest_handle_intel_pt_intr in generic code is a bit off.  Of 
course it has to be in the struct, but the wrapper might be placed in 
arch/x86/include/asm/perf_event.h as well (applies to patch 7 as well).

Paolo