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AJvYcCUG7l07T2bxh91DgUEMQ2o+X20ZIsrlFoiMymbFre8jc88Cr4B1briDCLUVxVy2R84ED2PA6rGEi/E=@vger.kernel.org X-Gm-Message-State: AOJu0YwdlCu9XC8NUh3iD+cDuDim43JgK1w3WMQsqeYd/NMLvPsOlMop q57MihOfHhpy/kBs9xHN3E8AWZiB8lTbLzuHFVJCdnn6mGHz80MIZczU09hVwy54/nqncUKbNln foQ== X-Google-Smtp-Source: AGHT+IHAKYyva2OQ2qZQzRH4TY78SgPHtJqed37fmibnibVOLNekS1q+MnqBaVU8gqhPocMC9s980/Kf1V4= X-Received: from pjd6.prod.google.com ([2002:a17:90b:54c6:b0:2ea:7174:2101]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3c42:b0:2ea:4480:e3e5 with SMTP id 98e67ed59e1d1-2ee08ed4488mr5835622a91.22.1732757679026; Wed, 27 Nov 2024 17:34:39 -0800 (PST) Reply-To: Sean Christopherson Date: Wed, 27 Nov 2024 17:33:31 -0800 In-Reply-To: <20241128013424.4096668-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-sgx@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241128013424.4096668-1-seanjc@google.com> X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241128013424.4096668-5-seanjc@google.com> Subject: [PATCH v3 04/57] KVM: x86: Explicitly do runtime CPUID updates "after" initial setup From: Sean Christopherson To: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Jarkko Sakkinen Cc: kvm@vger.kernel.org, linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org, Maxim Levitsky , Hou Wenlong , Xiaoyao Li , Kechen Lu , Oliver Upton , Binbin Wu , Yang Weijiang , Robert Hoo Explicitly perform runtime CPUID adjustments as part of the "after set CPUID" flow to guard against bugs where KVM consumes stale vCPU/CPUID state during kvm_update_cpuid_runtime(). E.g. see commit 4736d85f0d18 ("KVM: x86: Use actual kvm_cpuid.base for clearing KVM_FEATURE_PV_UNHALT"). Whacking each mole individually is not sustainable or robust, e.g. while the aforemention commit fixed KVM's PV features, the same issue lurks for Xen and Hyper-V features, Xen and Hyper-V simply don't have any runtime features (though spoiler alert, neither should KVM). Updating runtime features in the "full" path will also simplify adding a snapshot of the guest's capabilities, i.e. of caching the intersection of guest CPUID and kvm_cpu_caps (modulo a few edge cases). Signed-off-by: Sean Christopherson --- arch/x86/kvm/cpuid.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index b9ad07e24160..1944f9415672 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -157,6 +157,9 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu, return fpu_enable_guest_xfd_features(&vcpu->arch.guest_fpu, xfeatures); } +static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *entries, + int nent); + /* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */ static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, int nent) @@ -164,6 +167,17 @@ static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 struct kvm_cpuid_entry2 *orig; int i; + /* + * Apply runtime CPUID updates to the incoming CPUID entries to avoid + * false positives due mismatches on KVM-owned feature flags. Note, + * runtime CPUID updates may consume other CPUID-driven vCPU state, + * e.g. KVM or Xen CPUID bases. Updating runtime state before full + * CPUID processing is functionally correct only because any change in + * CPUID is disallowed, i.e. using stale data is ok because the below + * checks will reject the change. + */ + __kvm_update_cpuid_runtime(vcpu, e2, nent); + if (nent != vcpu->arch.cpuid_nent) return -EINVAL; @@ -348,6 +362,8 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) bitmap_zero(vcpu->arch.governed_features.enabled, KVM_MAX_NR_GOVERNED_FEATURES); + kvm_update_cpuid_runtime(vcpu); + /* * If TDP is enabled, let the guest use GBPAGES if they're supported in * hardware. The hardware page walker doesn't let KVM disable GBPAGES, @@ -429,8 +445,6 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, { int r; - __kvm_update_cpuid_runtime(vcpu, e2, nent); - /* * KVM does not correctly handle changing guest CPUID after KVM_RUN, as * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't