linux-kernel - Re: [PATCH v3 02/16] KVM: x86: Register perf callbacks after calling vendor's hardware

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Date:   Wed, 22 Sep 2021 08:23:25 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....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>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Cc:     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>,
        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-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.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 v3 02/16] KVM: x86: Register perf callbacks after calling
 vendor's hardware_setup()

On 22/09/21 02:05, Sean Christopherson wrote:
> Wait to register perf callbacks until after doing vendor hardaware setup.
> VMX's hardware_setup() configures Intel Processor Trace (PT) mode, and a
> future fix to register the Intel PT guest interrupt hook if and only if
> Intel PT is exposed to the guest will consume the configured PT mode.
> 
> Delaying registration to hardware setup is effectively a nop as KVM's perf
> hooks all pivot on the per-CPU current_vcpu, which is non-NULL only when
> KVM is handling an IRQ/NMI in a VM-Exit path.  I.e. current_vcpu will be
> NULL throughout both kvm_arch_init() and kvm_arch_hardware_setup().
> 
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Artem Kashkanov <artem.kashkanov@...el.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/x86.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 86539c1686fa..fb6015f97f9e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8426,8 +8426,6 @@ int kvm_arch_init(void *opaque)
>   
>   	kvm_timer_init();
>   
> -	perf_register_guest_info_callbacks(&kvm_guest_cbs);
> -
>   	if (boot_cpu_has(X86_FEATURE_XSAVE)) {
>   		host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
>   		supported_xcr0 = host_xcr0 & KVM_SUPPORTED_XCR0;
> @@ -8461,7 +8459,6 @@ void kvm_arch_exit(void)
>   		clear_hv_tscchange_cb();
>   #endif
>   	kvm_lapic_exit();
> -	perf_unregister_guest_info_callbacks(&kvm_guest_cbs);
>   
>   	if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
>   		cpufreq_unregister_notifier(&kvmclock_cpufreq_notifier_block,
> @@ -11064,6 +11061,8 @@ int kvm_arch_hardware_setup(void *opaque)
>   	memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
>   	kvm_ops_static_call_update();
>   
> +	perf_register_guest_info_callbacks(&kvm_guest_cbs);
> +
>   	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
>   		supported_xss = 0;
>   
> @@ -11091,6 +11090,8 @@ int kvm_arch_hardware_setup(void *opaque)
>   
>   void kvm_arch_hardware_unsetup(void)
>   {
> +	perf_unregister_guest_info_callbacks(&kvm_guest_cbs);
> +
>   	static_call(kvm_x86_hardware_unsetup)();
>   }
>   
> 

Acked-by: Paolo Bonzini <pbonzini@...hat.com>