KVM: VMX: Fix a wrong usage of vmcs_config

The function ept_update_paging_mode_cr0() write to
CPU_BASED_VM_EXEC_CONTROL based on vmcs_config.cpu_based_exec_ctrl. That's
wrong because the variable may not consistent with the content in the
CPU_BASE_VM_EXEC_CONTROL MSR.
Signed-off-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/vmx.c

@@ -1441,7 +1441,7 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
 	if (!(cr0 & X86_CR0_PG)) {
 		/* From paging/starting to nonpaging */
 		vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
-			     vmcs_config.cpu_based_exec_ctrl |
+			     vmcs_read32(CPU_BASED_VM_EXEC_CONTROL) |
 			     (CPU_BASED_CR3_LOAD_EXITING |
 			      CPU_BASED_CR3_STORE_EXITING));
 		vcpu->arch.cr0 = cr0;
@@ -1451,7 +1451,7 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
 	} else if (!is_paging(vcpu)) {
 		/* From nonpaging to paging */
 		vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
-			     vmcs_config.cpu_based_exec_ctrl &
+			     vmcs_read32(CPU_BASED_VM_EXEC_CONTROL) &
 			     ~(CPU_BASED_CR3_LOAD_EXITING |
 			       CPU_BASED_CR3_STORE_EXITING));
 		vcpu->arch.cr0 = cr0;