linux-kernel - Re: [PATCH] Move VMEnter and VMExit tracepoints closer to the actual event

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Date:   Thu, 20 May 2021 09:21:24 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Stefano De Venuto <stefano.devenuto99@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, x86@...nel.org,
        hpa@...or.com, kvm@...r.kernel.org, rostedt@...dmis.org,
        y.karadz@...il.com,
        Stefano De Venuto <stefano.devenuto99@...il.com>,
        Dario Faggioli <dfaggioli@...e.com>
Subject: Re: [PATCH] Move VMEnter and VMExit tracepoints closer to the actual event

On Wed, May 19 2021 at 20:23, Stefano De Venuto wrote:
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 05eca131eaf2..c77d4866e239 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3275,8 +3275,6 @@ static int handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>  	struct kvm_run *kvm_run = vcpu->run;
>  	u32 exit_code = svm->vmcb->control.exit_code;
>  
> -	trace_kvm_exit(exit_code, vcpu, KVM_ISA_SVM);
> -
>  	/* SEV-ES guests must use the CR write traps to track CR registers. */
>  	if (!sev_es_guest(vcpu->kvm)) {
>  		if (!svm_is_intercept(svm, INTERCEPT_CR0_WRITE))
> @@ -3707,6 +3705,8 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
>  
>  	kvm_guest_enter_irqoff();
>  
> +	trace_kvm_entry(vcpu);

No. This violates the noinstr rules and will make objtool complain on a
full validation run.

So this wants to be:

+       instrumentation_begin();
+	trace_kvm_entry(vcpu);
+       instrumentation_end();

  	kvm_guest_enter_irqoff();

and on the exit side the trace wants to be post kvm_guest_exit_irqoff().

Thanks,

        tglx