Messages in this thread Patch in this message | | | From | Sean Christopherson <> | Subject | [RFC PATCH 18/21] KVM: x86: Invoke kvm_x86_ops->cpuid_update() after kvm_update_cpuid() | Date | Fri, 26 Jul 2019 22:52:11 -0700 |
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VMX's virtualization of SGX adds a lovely dependency on the guest's supported xcr0, which is calculated in kvm_update_cpuid(). VMX must toggled its interception of SGX instructions based on the supported xcr0, i.e. kvm_x86_ops->cpuid_update() is certainly the correct location for the dependent code.
kvm_update_cpuid() was originally added by commit 2acf923e38fb ("KVM: VMX: Enable XSAVE/XRSTOR for guest"). There is no indication that its placement after kvm_x86_ops->cpuid_update() was anything more than a "new function at the end" decision.
Inspection of the current code reveals no dependency on kvm_x86_ops's cpuid_update() in kvm_update_cpuid() or any of its helpers.
- SVM's sole update is to conditionally clear X86_FEATURE_X2APIC. X86_FEATURE_X2APIC is only consumed by kvm_apic_set_state(), which is already called immediately prior to kvm_x86_ops->cpuid_update().
- VMX updates only nested VMX MSRs, allowed FEATURE_CONTROL bits, and VMCS fields, e.g. secondary execution controls, none of which should bleed back into kvm_update_cpuid() barring an egregious dependency bug somewhere else.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> --- arch/x86/kvm/cpuid.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 70e488951f25..4c235af5318c 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -222,8 +222,9 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu, vcpu->arch.cpuid_nent = cpuid->nent; cpuid_fix_nx_cap(vcpu); kvm_apic_set_version(vcpu); - kvm_x86_ops->cpuid_update(vcpu); r = kvm_update_cpuid(vcpu); + if (!r) + kvm_x86_ops->cpuid_update(vcpu); out: vfree(cpuid_entries); @@ -245,8 +246,9 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu, goto out; vcpu->arch.cpuid_nent = cpuid->nent; kvm_apic_set_version(vcpu); - kvm_x86_ops->cpuid_update(vcpu); r = kvm_update_cpuid(vcpu); + if (!r) + kvm_x86_ops->cpuid_update(vcpu); out: return r; } -- 2.22.0
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