KVM: nVMX: Explicitly check for valid guest state for !unrestricted guest

Call guest_state_valid() directly instead of querying emulation_required
when checking if L1 is attempting VM-Enter with invalid guest state.
If emulate_invalid_guest_state is false, KVM will fixup segment regs to
avoid emulation and will never set emulation_required, i.e. KVM will
incorrectly miss the associated consistency checks because the nested
path stuffs segments directly into vmcs02.

Opportunsitically add Consistency Check tracing to make future debug
suck a little less.

Fixes: 2bb8cafe ("KVM: vVMX: signal failure for nested VMEntry if emulation_required")
Fixes: 3184a995 ("KVM: nVMX: fix vmentry failure code when L2 state would require emulation")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923184452.980-4-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -2576,7 +2576,7 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 	 * which means L1 attempted VMEntry to L2 with invalid state.
 	 * Fail the VMEntry.
 	 */
-	if (vmx->emulation_required) {
+	if (CC(!vmx_guest_state_valid(vcpu))) {
 		*entry_failure_code = ENTRY_FAIL_DEFAULT;
 		return -EINVAL;
 	}

arch/x86/kvm/vmx/vmx.c

@@ -337,7 +337,6 @@ static const struct kernel_param_ops vmentry_l1d_flush_ops = {
 };
 module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
 
-static bool guest_state_valid(struct kvm_vcpu *vcpu);
 static u32 vmx_segment_access_rights(struct kvm_segment *var);
 static __always_inline void vmx_disable_intercept_for_msr(unsigned long *msr_bitmap,
 							  u32 msr, int type);
@@ -1340,7 +1339,7 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 
 static bool emulation_required(struct kvm_vcpu *vcpu)
 {
-	return emulate_invalid_guest_state && !guest_state_valid(vcpu);
+	return emulate_invalid_guest_state && !vmx_guest_state_valid(vcpu);
 }
 
 unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
@@ -3402,11 +3401,8 @@ static bool cs_ss_rpl_check(struct kvm_vcpu *vcpu)
  * not.
  * We assume that registers are always usable
  */
-static bool guest_state_valid(struct kvm_vcpu *vcpu)
+bool __vmx_guest_state_valid(struct kvm_vcpu *vcpu)
 {
-	if (is_unrestricted_guest(vcpu))
-		return true;
-
 	/* real mode guest state checks */
 	if (!is_protmode(vcpu) || (vmx_get_rflags(vcpu) & X86_EFLAGS_VM)) {
 		if (!rmode_segment_valid(vcpu, VCPU_SREG_CS))

arch/x86/kvm/vmx/vmx.h

@@ -321,6 +321,7 @@ void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa,
 		   int root_level);
+
 void update_exception_bitmap(struct kvm_vcpu *vcpu);
 void vmx_update_msr_bitmap(struct kvm_vcpu *vcpu);
 bool vmx_nmi_blocked(struct kvm_vcpu *vcpu);
@@ -472,6 +473,12 @@ static inline bool is_unrestricted_guest(struct kvm_vcpu *vcpu)
 	    SECONDARY_EXEC_UNRESTRICTED_GUEST));
 }
 
+bool __vmx_guest_state_valid(struct kvm_vcpu *vcpu);
+static inline bool vmx_guest_state_valid(struct kvm_vcpu *vcpu)
+{
+	return is_unrestricted_guest(vcpu) || __vmx_guest_state_valid(vcpu);
+}
+
 void dump_vmcs(void);
 
 #endif /* __KVM_X86_VMX_H */