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[PATCH v2 03/15] VMX: don't run with CR4.VMXE set when VMX could not be enabled


  • To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 24 Nov 2023 09:37:55 +0100
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  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>
  • Delivery-date: Fri, 24 Nov 2023 08:38:01 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
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.
---
v2: Actually clear CR4.VMXE for the BSP on the error path.

--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2959,14 +2959,18 @@ 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() )
     {
+        write_cr4(read_cr4() & ~X86_CR4_VMXE);
         printk("VMX: failed to initialise.\n");
         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 )




 


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