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AJvYcCWwYAxjztwBFGS6luU8wreYpsDP1pXqRe7BnozBNwuyfixI+hmzKOtu5uF9LeHv1xRYLoToVZV1S40eJzo=@vger.kernel.org X-Gm-Message-State: AOJu0YyrcYs9vVVs6ZNLpmM91FHVzpYNtTR5M6XCrtMga5M/kzuHI0zQ omhOu+4vqOlW3V1Ro38j115ky8NaqOA6asNDk3GT4nrNxxiNhdVioSDBKDzOA3kev7zl3F0BCpi MTu2ctA== X-Google-Smtp-Source: AGHT+IFvFrLqHR1ghrQGa/UNDi1qRfKtC9i6a3FVhMJPpt61M52gk1rUWTLvFny4IIdNm62PLyCcaiVBrlM= X-Received: from pjbqb9.prod.google.com ([2002:a17:90b:2809:b0:2ef:d283:5089]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3f8c:b0:311:df4b:4b81 with SMTP id 98e67ed59e1d1-313470578eamr495536a91.25.1749141559893; Thu, 05 Jun 2025 09:39:19 -0700 (PDT) Date: Thu, 5 Jun 2025 09:39:18 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250529234013.3826933-1-seanjc@google.com> <20250529234013.3826933-18-seanjc@google.com> Message-ID: Subject: Re: [PATCH 17/28] KVM: SVM: Manually recalc all MSR intercepts on userspace MSR filter change From: Sean Christopherson To: Chao Gao Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Borislav Petkov , Xin Li , Dapeng Mi Content-Type: text/plain; charset="us-ascii" On Thu, Jun 05, 2025, Chao Gao wrote: > >+static void svm_recalc_msr_intercepts(struct kvm_vcpu *vcpu) > >+{ > >+ struct vcpu_svm *svm = to_svm(vcpu); > >+ > >+ svm_vcpu_init_msrpm(vcpu); > >+ > >+ if (lbrv) > >+ svm_recalc_lbr_msr_intercepts(vcpu); > >+ > >+ if (boot_cpu_has(X86_FEATURE_IBPB)) > >+ svm_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W, > >+ !guest_has_pred_cmd_msr(vcpu)); > >+ > >+ if (boot_cpu_has(X86_FEATURE_FLUSH_L1D)) > >+ svm_set_intercept_for_msr(vcpu, MSR_IA32_FLUSH_CMD, MSR_TYPE_W, > >+ !guest_cpu_cap_has(vcpu, X86_FEATURE_FLUSH_L1D)); > >+ > >+ /* > >+ * Unconditionally disable interception of SPEC_CTRL if V_SPEC_CTRL is > >+ * supported, i.e. if VMRUN/#VMEXIT context switch MSR_IA32_SPEC_CTRL. > >+ */ Tangentially related, the comment above isn't quite correct. MSR_IA32_SPEC_CTRL isn't purely context switched, the CPU merges together host and guest values. Same end result though: KVM doesn't need to manually context switch the MSR. > >+ if (boot_cpu_has(X86_FEATURE_V_SPEC_CTRL)) > >+ svm_disable_intercept_for_msr(vcpu, MSR_IA32_SPEC_CTRL, MSR_TYPE_RW); > > I think there is a bug in the original code. KVM should inject #GP when guests > try to access unsupported MSRs. Specifically, a guest w/o spec_ctrl support > should get #GP when it tries to access the MSR regardless of V_SPEC_CTRL > support on the host. > > So, here should be > > if (boot_cpu_has(X86_FEATURE_V_SPEC_CTRL)) > svm_set_intercept_for_msr(vcpu, MSR_IA32_SPEC_CTRL, MSR_TYPE_RW, > !guest_has_spec_ctrl_msr(vcpu)); Right you are! I'll slot in a patch earlier in the series, and then it'll end up looking like this. I'll also post a KUT testcase.