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Thu, 19 Dec 2024 09:33:02 -0800 (PST) X-Google-Smtp-Source: AGHT+IHDhWPk5NquZCFc8ici3TtWRL10EJUEBD7cwlMDdiHiO+vTqp4HxfbdaH2FEJ4LeEcClsDMmA== X-Received: by 2002:a05:600c:4302:b0:435:edb0:5d27 with SMTP id 5b1f17b1804b1-4365c775131mr36784025e9.9.1734629581747; Thu, 19 Dec 2024 09:33:01 -0800 (PST) Received: from [192.168.1.84] ([93.56.163.127]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-43656b11d1dsm57919885e9.25.2024.12.19.09.33.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 09:33:01 -0800 (PST) Message-ID: <9ff2be87-117a-4f96-af3b-dacb55467449@redhat.com> Date: Thu, 19 Dec 2024 18:33:00 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 3/3] KVM: x86: add new nested vmexit tracepoints To: Maxim Levitsky , kvm@vger.kernel.org Cc: x86@kernel.org, Dave Hansen , Thomas Gleixner , Borislav Petkov , Ingo Molnar , Sean Christopherson , "H. Peter Anvin" , linux-kernel@vger.kernel.org References: <20240910200350.264245-1-mlevitsk@redhat.com> <20240910200350.264245-4-mlevitsk@redhat.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: <20240910200350.264245-4-mlevitsk@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/10/24 22:03, 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 > --- > arch/x86/kvm/svm/nested.c | 22 +++++++++++ > arch/x86/kvm/trace.h | 82 +++++++++++++++++++++++++++++++++++++-- > arch/x86/kvm/vmx/nested.c | 27 +++++++++++++ > arch/x86/kvm/x86.c | 3 ++ > 4 files changed, 131 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c > index 6f704c1037e51..2020307481553 100644 > --- a/arch/x86/kvm/svm/nested.c > +++ b/arch/x86/kvm/svm/nested.c > @@ -38,6 +38,8 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu, > { > struct vcpu_svm *svm = to_svm(vcpu); > struct vmcb *vmcb = svm->vmcb; > + u64 host_error_code = vmcb->control.exit_info_1; > + > > if (vmcb->control.exit_code != SVM_EXIT_NPF) { > /* > @@ -48,11 +50,15 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu, > vmcb->control.exit_code_hi = 0; > vmcb->control.exit_info_1 = (1ULL << 32); > vmcb->control.exit_info_2 = fault->address; > + host_error_code = 0; > } > > vmcb->control.exit_info_1 &= ~0xffffffffULL; > vmcb->control.exit_info_1 |= fault->error_code; > > + trace_kvm_nested_page_fault(fault->address, host_error_code, > + fault->error_code); > + I disagree with Sean about trace_kvm_nested_page_fault. It's a useful addition and it is easier to understand what's happening with a dedicated tracepoint (especially on VMX). Tracepoint are not an exact science and they aren't entirely kernel API. At least they can just go away at any time (changing them is a lot more tricky, but their presence is not guaranteed). The one below has the slight ugliness of having to do some computation in nested_svm_vmexit(), this one should go in. > nested_svm_vmexit(svm); > } > > @@ -1126,6 +1132,22 @@ 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 & 0xFFFFFFFFull) | > + (((u64)kvm_rdx_read(vcpu) << 32))); > + break; > + case SVM_EXIT_VMMCALL: > + trace_kvm_nested_hypercall(vmcb12->save.rax, > + kvm_rbx_read(vcpu), > + kvm_rcx_read(vcpu), > + kvm_rdx_read(vcpu)); > + break; Here I probably would have preferred an unconditional tracepoint giving RAX/RBX/RCX/RDX after a nested vmexit. This is not exactly what Sean wanted but perhaps it strikes a middle ground? I know you wrote this for a debugging tool, do you really need to have everything in a single tracepoint, or can you correlate the existing exit tracepoint with this hypothetical trace_kvm_nested_exit_regs, to pick RDMSR vs. WRMSR? Paolo