KVM: VMX: Drop guest CPUID check for VMXE in vmx_set_cr4()

Drop vmx_set_cr4()'s somewhat hidden guest_cpuid_has() check on VMXE now
that common x86 handles the check by incorporating VMXE into the CR4
reserved bits, i.e. in cr4_guest_rsvd_bits.  This fixes a bug where KVM
incorrectly rejects KVM_SET_SREGS with CR4.VMXE=1 if it's executed
before KVM_SET_CPUID{,2}.

Fixes: 5e1746d6205d ("KVM: nVMX: Allow setting the VMXE bit in CR4")
Reported-by: Stas Sergeev <stsp@users.sourceforge.net>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20201007014417.29276-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 47b8357..7ebf08d 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3129,9 +3129,10 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
                 * must first be able to turn on cr4.VMXE (see handle_vmon()).
                 * So basically the check on whether to allow nested VMX
                 * is here.  We operate under the default treatment of SMM,
-                * so VMX cannot be enabled under SMM.
+                * so VMX cannot be enabled under SMM.  Note, guest CPUID is
+                * intentionally ignored, it's handled by cr4_guest_rsvd_bits.
                 */
-               if (!nested_vmx_allowed(vcpu) || is_smm(vcpu))
+               if (!nested || is_smm(vcpu))
                        return 1;
        }