Re: [PATCH v3 02/16] KVM: x86: Register perf callbacks after calling vendor's hardware_setup()

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

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@xxxxxxxxxxxxxxx>
> Cc: Artem Kashkanov <artem.kashkanov@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   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@xxxxxxxxxx>