linux-kernel - Re: [PATCH 6/7] KVM: x86: Use common definition for kvm_nested

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Date:   Mon, 20 Jul 2020 17:27:17 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 6/7] KVM: x86: Use common definition for
 kvm_nested_vmexit tracepoint

On Mon, Jul 20, 2020 at 06:52:15PM +0200, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@...el.com> writes:
> > +TRACE_EVENT_KVM_EXIT(kvm_nested_vmexit);
> >  
> >  /*
> >   * Tracepoint for #VMEXIT reinjected to the guest
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index fc70644b916ca..f437d99f4db09 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -5912,10 +5912,7 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
> >  	exit_intr_info = vmx_get_intr_info(vcpu);
> >  	exit_qual = vmx_get_exit_qual(vcpu);
> >  
> > -	trace_kvm_nested_vmexit(vcpu, exit_reason, exit_qual,
> > -				vmx->idt_vectoring_info, exit_intr_info,
> > -				vmcs_read32(VM_EXIT_INTR_ERROR_CODE),
> > -				KVM_ISA_VMX);
> > +	trace_kvm_nested_vmexit(exit_reason, vcpu, KVM_ISA_VMX);
> >  
> >  	/* If L0 (KVM) wants the exit, it trumps L1's desires. */
> >  	if (nested_vmx_l0_wants_exit(vcpu, exit_reason))
> 
> With so many lines removed I'm almost in love with the patch! However,
> when testing on SVM (unrelated?) my trace log looks a bit ugly:
> 
>            <...>-315119 [010]  3733.092646: kvm_nested_vmexit:    CAN'T FIND FIELD "rip"<CANT FIND FIELD exit_code>vcpu 0 reason npf rip 0x400433 info1 0x0000000200000006 info2 0x0000000000641000 intr_info 0x00000000 error_code 0x00000000
>            <...>-315119 [010]  3733.092655: kvm_nested_vmexit:    CAN'T FIND FIELD "rip"<CANT FIND FIELD exit_code>vcpu 0 reason npf rip 0x400433 info1 0x0000000100000014 info2 0x0000000000400000 intr_info 0x00000000 error_code 0x00000000
> 
> ...
> 
> but after staring at this for some time I still don't see where this
> comes from :-( ... but reverting this commit helps:

The CAN'T FIND FIELD blurb comes from tools/lib/traceevent/event-parse.c.

I assume you are using tooling of some form to generate the trace, i.e. the
issue doesn't show up in /sys/kernel/debug/tracing/trace.  If that's the
case, this is more or less ABI breakage :-(
 
>  qemu-system-x86-9928  [022]   379.260656: kvm_nested_vmexit:    rip 400433 reason EXIT_NPF info1 200000006 info2 641000 int_info 0 int_info_err 0
>  qemu-system-x86-9928  [022]   379.260666: kvm_nested_vmexit:    rip 400433 reason EXIT_NPF info1 100000014 info2 400000 int_info 0 int_info_err 0
> 
> -- 
> Vitaly
>