x86/vmx: Use asm goto() in _vmx_cpu_up()

With the new toolchain baseline, we can make use of asm goto() in certain
places, and the VMXON invocation is one example.

This removes the logic to set up rc (including a fixup section where bactraces
have no connection to the invoking function), the logic to decode it,
including the default case which was dead but not visibly-so to the compiler.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/vmx/vmcs.c

@@ -749,30 +749,15 @@ static int _vmx_cpu_up(bool bsp)
     if ( bsp && (rc = vmx_cpu_up_prepare(cpu)) != 0 )
         return rc;
 
-    switch ( __vmxon(this_cpu(vmxon_region)) )
-    {
-    case -2: /* #UD or #GP */
-        if ( bios_locked &&
-             test_bit(X86_FEATURE_SMX, &boot_cpu_data.x86_capability) &&
-             (!(eax & IA32_FEATURE_CONTROL_ENABLE_VMXON_OUTSIDE_SMX) ||
-              !(eax & IA32_FEATURE_CONTROL_ENABLE_VMXON_INSIDE_SMX)) )
-        {
-            printk("CPU%d: VMXON failed: perhaps because of TXT settings "
-                   "in your BIOS configuration?\n", cpu);
-            printk(" --> Disable TXT in your BIOS unless using a secure "
-                   "bootloader.\n");
-            return -EINVAL;
-        }
-        /* fall through */
-    case -1: /* CF==1 or ZF==1 */
-        printk("CPU%d: unexpected VMXON failure\n", cpu);
-        return -EINVAL;
-    case 0: /* success */
-        this_cpu(vmxon) = 1;
-        break;
-    default:
-        BUG();
-    }
+    asm goto ( "1: vmxon %[addr]\n\t"
+               "   jbe %l[vmxon_fail]\n\t"
+               _ASM_EXTABLE(1b, %l[vmxon_fault])
+               :
+               : [addr] "m" (this_cpu(vmxon_region))
+               : "memory"
+               : vmxon_fail, vmxon_fault );
+
+    this_cpu(vmxon) = 1;
 
     hvm_asid_init(cpu_has_vmx_vpid ? (1u << VMCS_VPID_WIDTH) : 0);
 
@@ -785,6 +770,24 @@ static int _vmx_cpu_up(bool bsp)
     vmx_pi_per_cpu_init(cpu);
 
     return 0;
+
+ vmxon_fault:
+    if ( bios_locked &&
+         test_bit(X86_FEATURE_SMX, &boot_cpu_data.x86_capability) &&
+         (!(eax & IA32_FEATURE_CONTROL_ENABLE_VMXON_OUTSIDE_SMX) ||
+          !(eax & IA32_FEATURE_CONTROL_ENABLE_VMXON_INSIDE_SMX)) )
+    {
+        printk(XENLOG_ERR
+               "CPU%d: VMXON failed: perhaps because of TXT settings in your BIOS configuration?\n",
+               cpu);
+        printk(XENLOG_ERR
+               " --> Disable TXT in your BIOS unless using a secure bootloader.\n");
+        return -EINVAL;
+    }
+
+ vmxon_fail:
+    printk(XENLOG_ERR "CPU%d: unexpected VMXON failure\n", cpu);
+    return -EINVAL;
 }
 
 int cf_check vmx_cpu_up(void)

xen/arch/x86/include/asm/hvm/vmx/vmx.h

@@ -559,25 +559,6 @@ static inline void __vmxoff(void)
         : : : "memory" );
 }
 
-static inline int __vmxon(u64 addr)
-{
-    int rc;
-
-    asm volatile ( 
-        "1: " VMXON_OPCODE MODRM_EAX_06 "\n"
-        "   setna %b0 ; neg %0\n" /* CF==1 or ZF==1 --> rc = -1 */
-        "2:\n"
-        ".section .fixup,\"ax\"\n"
-        "3: sub $2,%0 ; jmp 2b\n"    /* #UD or #GP --> rc = -2 */
-        ".previous\n"
-        _ASM_EXTABLE(1b, 3b)
-        : "=q" (rc)
-        : "0" (0), "a" (&addr)
-        : "memory");
-
-    return rc;
-}
-
 int cf_check vmx_guest_x86_mode(struct vcpu *v);
 unsigned int vmx_get_cpl(void);