x86/emul: Rearrange the logic in hvmemul_{read,write}_cr()

In hvmemul_read_cr(), make the TRACE()/X86EMUL_OKAY path common in preparation
for adding a %cr8 case.  Use a local 'val' variable instead of always
operating on a deferenced pointer.

In both, calculate curr once.

No functional change.

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

xen/arch/x86/hvm/emulate.c

@@ -2273,23 +2273,30 @@ static int cf_check hvmemul_write_io(
 
 static int cf_check hvmemul_read_cr(
     unsigned int reg,
-    unsigned long *val,
+    unsigned long *pval,
     struct x86_emulate_ctxt *ctxt)
 {
+    struct vcpu *curr = current;
+    unsigned long val;
+
     switch ( reg )
     {
     case 0:
     case 2:
     case 3:
     case 4:
-        *val = current->arch.hvm.guest_cr[reg];
-        TRACE(TRC_HVM_CR_READ64, reg, *val, *val >> 32);
-        return X86EMUL_OKAY;
-    default:
+        val = curr->arch.hvm.guest_cr[reg];
         break;
+
+    default:
+        return X86EMUL_UNHANDLEABLE;
     }
 
-    return X86EMUL_UNHANDLEABLE;
+    TRACE(TRC_HVM_CR_READ64, reg, val, val >> 32);
+
+    *pval = val;
+
+    return X86EMUL_OKAY;
 }
 
 static int cf_check hvmemul_write_cr(
@@ -2297,6 +2304,7 @@ static int cf_check hvmemul_write_cr(
     unsigned long val,
     struct x86_emulate_ctxt *ctxt)
 {
+    struct vcpu *curr = current;
     int rc;
 
     TRACE(TRC_HVM_CR_WRITE64, reg, val, val >> 32);
@@ -2307,13 +2315,13 @@ static int cf_check hvmemul_write_cr(
         break;
 
     case 2:
-        current->arch.hvm.guest_cr[2] = val;
+        curr->arch.hvm.guest_cr[2] = val;
         rc = X86EMUL_OKAY;
         break;
 
     case 3:
     {
-        bool noflush = hvm_pcid_enabled(current) && (val & X86_CR3_NOFLUSH);
+        bool noflush = hvm_pcid_enabled(curr) && (val & X86_CR3_NOFLUSH);
 
         if ( noflush )
             val &= ~X86_CR3_NOFLUSH;