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

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Date:   Tue, 21 Jul 2020 15:59:06 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.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

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> 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 :-(
>  

Right you are,

the tool is called 'trace-cmd record -e kvm ...' / 'trace-cmd report'
but I always thought it's not any different from looking at
/sys/kernel/debug/tracing/trace directly. Apparently I was wrong. 'cat
/sys/kernel/debug/tracing/trace' seems to be OK, e.g.:

 qemu-system-x86-20263 [006] .... 75982.292657: kvm_nested_vmexit: vcpu 0 reason hypercall rip 0x40122f info1 0x0000000000000000 info2 0x0000000000000000 intr_info 0x00000000 error_code 0x00000000

-- 
Vitaly