... or we fail to enable the functionality on the BSP for other reasons.
The only place where hardware announcing the feature is recorded is the
raw CPU policy/featureset.

Inspired by https://lore.kernel.org/all/20230921114940.957141-1-pbonzini@redhat.com/.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2543,6 +2543,7 @@ const struct hvm_function_table * __init
 
     if ( _svm_cpu_up(true) )
     {
+        setup_clear_cpu_cap(X86_FEATURE_SVM);
         printk("SVM: failed to initialise.\n");
         return NULL;
     }
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -2162,6 +2162,23 @@ int __init vmx_vmcs_init(void)
 
     if ( !ret )
         register_keyhandler('v', vmcs_dump, "dump VT-x VMCSs", 1);
+    else
+    {
+        setup_clear_cpu_cap(X86_FEATURE_VMX);
+
+        /*
+         * _vmx_vcpu_up() may have made it past feature identification.
+         * Make sure all dependent features are off as well.
+         */
+        vmx_basic_msr              = 0;
+        vmx_pin_based_exec_control = 0;
+        vmx_cpu_based_exec_control = 0;
+        vmx_secondary_exec_control = 0;
+        vmx_vmexit_control         = 0;
+        vmx_vmentry_control        = 0;
+        vmx_ept_vpid_cap           = 0;
+        vmx_vmfunc                 = 0;
+    }
 
     return ret;
 }