[PATCH 2/2] KVM: VMX: Add knob to allow rejecting kvm_intel on inconsistent VMCS config

[Sean Christopherson <seanjc@google.com>]

Add an off-by-default module param, reject_inconsistent_vmcs_config, to
allow rejecting the load of kvm_intel if an inconsistent VMCS config is
detected.  Continuing on with an inconsistent, degraded config is
undesirable when the CPU is expected to support a given set of features,
e.g. can result in a misconfigured VM if userspace doesn't cross-check
KVM_GET_SUPPORTED_CPUID, and/or can result in poor performance due to
lack of fast MSR switching.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2ea256de9aba..11413a8cc57f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -119,6 +119,9 @@ module_param(nested, bool, S_IRUGO);
 bool __read_mostly enable_pml = 1;
 module_param_named(pml, enable_pml, bool, S_IRUGO);
 
+static bool __read_mostly reject_inconsistent_vmcs_config;
+module_param(reject_inconsistent_vmcs_config, bool, 0444);
+
 static bool __read_mostly dump_invalid_vmcs = 0;
 module_param(dump_invalid_vmcs, bool, 0644);
 
@@ -2577,15 +2580,23 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 					     CPU_BASED_CR3_STORE_EXITING |
 					     CPU_BASED_INVLPG_EXITING);
 	} else if (vmx_cap->ept) {
-		vmx_cap->ept = 0;
 		pr_warn_once("EPT CAP should not exist if not support "
 				"1-setting enable EPT VM-execution control\n");
+
+		if (reject_inconsistent_vmcs_config)
+			return -EIO;
+
+		vmx_cap->ept = 0;
 	}
 	if (!(_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_VPID) &&
-		vmx_cap->vpid) {
-		vmx_cap->vpid = 0;
+	    vmx_cap->vpid) {
 		pr_warn_once("VPID CAP should not exist if not support "
 				"1-setting enable VPID VM-execution control\n");
+
+		if (reject_inconsistent_vmcs_config)
+			return -EIO;
+
+		vmx_cap->vpid = 0;
 	}
 
 	if (_cpu_based_exec_control & CPU_BASED_ACTIVATE_TERTIARY_CONTROLS) {
@@ -2645,6 +2656,9 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 		pr_warn_once("Inconsistent VM-Entry/VM-Exit pair, entry = %x, exit = %x\n",
 			     _vmentry_control & n_ctrl, _vmexit_control & x_ctrl);
 
+		if (reject_inconsistent_vmcs_config)
+			return -EIO;
+
 		_vmentry_control &= ~n_ctrl;
 		_vmexit_control &= ~x_ctrl;
 	}
-- 
2.36.1.124.g0e6072fb45-goog