References: bsc#1214700

# Commit 0b5f149338e35a795bf609ce584640b0977f9e6c
# Date 2024-01-09 14:06:34 +0100
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/HVM: hide SVM/VMX when their enabling is prohibited by firmware

... 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
@@ -1708,6 +1708,7 @@ 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/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2553,6 +2553,21 @@ const struct hvm_function_table * __init
 
     if ( _vmx_cpu_up(true) )
     {
+        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;
+
         printk("VMX: failed to initialise.\n");
         return NULL;
     }
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -376,6 +376,8 @@ extern u64 vmx_basic_msr;
 /* VMFUNC leaf definitions */
 #define VMX_VMFUNC_EPTP_SWITCHING   (1ULL << 0)
 
+extern u64 vmx_vmfunc;
+
 /* VMCS field encodings. */
 #define VMCS_HIGH(x) ((x) | 1)
 enum vmcs_field {