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

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Message-ID: <a10d3a01-939c-493c-b93c-b3821735e062@redhat.com>
Date:   Fri, 24 Nov 2023 17:11:36 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...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 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

Paolo