linux-kernel - Re: [PATCH v3 4/4] KVM: x86: add new nested vmexit tracepoints

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Message-ID: <69607670cc11c05658870ae07d1af543a9446fe8.camel@redhat.com>
Date:   Tue, 28 Nov 2023 08:42:40 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 4/4] KVM: x86: add new nested vmexit tracepoints

On Fri, 2023-11-24 at 17:11 +0100, Paolo Bonzini wrote:
> On 9/28/23 12:36, Maxim Levitsky wrote:
> > Add 3 new tracepoints for nested VM exits which are intended
> > to capture extra information to gain insights about the nested guest
> > behavior.
> > 
> > The new tracepoints are:
> > 
> > - kvm_nested_msr
> > - kvm_nested_hypercall
> > 
> > These tracepoints capture extra register state to be able to know
> > which MSR or which hypercall was done.
> > 
> > - kvm_nested_page_fault
> > 
> > This tracepoint allows to capture extra info about which host pagefault
> > error code caused the nested page fault.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> 
> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
> 
> with just one question below that can be fixed when applying:
> 
> > @@ -1139,6 +1145,22 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> >   				       vmcb12->control.exit_int_info_err,
> >   				       KVM_ISA_SVM);
> >   
> > +	/* Collect some info about nested VM exits */
> > +	switch (vmcb12->control.exit_code) {
> > +	case SVM_EXIT_MSR:
> > +		trace_kvm_nested_msr(vmcb12->control.exit_info_1 == 1,
> > +				     kvm_rcx_read(vcpu),
> > +				     (vmcb12->save.rax & -1u) |
> > +				     (((u64)(kvm_rdx_read(vcpu) & -1u) << 32)));
> 
> Why the second "& -1u"?  (And I also prefer 0xFFFFFFFFull

I think I copied it from somewhere but I can't seem to find where.
I agree with both remarks, will fix.

Thanks,
	Best regards,
		Maxim Levitsky
> 
> Paolo
>