[PATCH 3/5] VMX: don't run with CR4.VMXE set when VMX could not be enabled

From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
	"Kevin Tian" <kevin.tian@intel.com>,
	"Jun Nakajima" <jun.nakajima@intel.com>
Subject: [PATCH 3/5] VMX: don't run with CR4.VMXE set when VMX could not be enabled
Date: Thu, 16 Nov 2023 14:32:07 +0100	[thread overview]
Message-ID: <d6a8ce0e-fcd9-4391-83c1-d9f709ada3f1@suse.com> (raw)
In-Reply-To: <791a9f45-2bed-48f9-af6a-9fbde65bcc71@suse.com>

While generally benign, doing so is still at best misleading.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
Using set_in_cr4() seems favorable over updating mmu_cr4_features
despite the resulting redundant CR4 update. But I certainly could be
talked into going the alternative route.

--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2959,7 +2959,7 @@ static bool __init has_if_pschange_mc(vo
 
 const struct hvm_function_table * __init start_vmx(void)
 {
-    set_in_cr4(X86_CR4_VMXE);
+    write_cr4(read_cr4() | X86_CR4_VMXE);
 
     if ( vmx_vmcs_init() )
     {
@@ -2967,6 +2967,9 @@ const struct hvm_function_table * __init
         return NULL;
     }
 
+    /* Arrange for APs to have CR4.VMXE set early on. */
+    set_in_cr4(X86_CR4_VMXE);
+
     vmx_function_table.singlestep_supported = cpu_has_monitor_trap_flag;
 
     if ( cpu_has_vmx_dt_exiting )


