From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: Invalid op code emulation for HVM guest and GPF
Date: Fri, 23 Mar 2012 19:58:19 +0000
Message-ID: <4F6CD5DB.6090806@citrix.com>
References: <20120323114425.07bd6db7@mantra.us.oracle.com>	<4F6CCD1A.4090505@citrix.com>	<20120323123042.5ebc0e18@mantra.us.oracle.com>
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To: Mukesh Rathor <mukesh.rathor@oracle.com>
Cc: "Xen-devel@lists.xensource.com" <Xen-devel@lists.xensource.com>, "kris.van.hees@oracle.com" <kris.van.hees@oracle.com>, Keir Fraser <keir.xen@gmail.com>
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On 23/03/12 19:38, Andrew Cooper wrote:
> Sadly, given your other email, I doubt it will work, because of the big
> catch all regarding the lock prefix.
>
> A brief scan over the Intel manuals and I cant see a case where an
> incorrect LOCK prefix would cause #GPF rather than #UD.
>
> Perhaps try changing it to EXP_UD instead of EXP_GP.  (Although I make
> no guarantee that this wont cause a lot of things to break.)

Try this patch instead.

I have still yet to find a single example in either manual 2A or B where
an invalid lock prefix would cause a #GPF rather than #UD

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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diff -r 0ecb8ffe61b2 xen/arch/x86/x86_emulate/x86_emulate.c
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1429,7 +1429,7 @@ x86_emulate(
     }
 
     /* Lock prefix is allowed only on RMW instructions. */
-    generate_exception_if((d & Mov) && lock_prefix, EXC_GP, 0);
+    generate_exception_if((d & Mov) && lock_prefix, EXC_UD, 0);
 
     /* ModRM and SIB bytes. */
     if ( d & ModRM )
@@ -1712,12 +1712,12 @@ x86_emulate(
             lock_prefix &&
             ((b < 0x20) || (b > 0x23)) && /* MOV CRn/DRn */
             (b != 0xc7),                  /* CMPXCHG{8,16}B */
-            EXC_GP, 0);
+            EXC_UD, 0);
         dst.type = OP_NONE;
         break;
 
     case DstReg:
-        generate_exception_if(lock_prefix, EXC_GP, 0);
+        generate_exception_if(lock_prefix, EXC_UD, 0);
         dst.type = OP_REG;
         if ( d & ByteOp )
         {
@@ -1773,7 +1773,7 @@ x86_emulate(
         dst = ea;
         if ( dst.type == OP_REG )
         {
-            generate_exception_if(lock_prefix, EXC_GP, 0);
+            generate_exception_if(lock_prefix, EXC_UD, 0);
             switch ( dst.bytes )
             {
             case 1: dst.val = *(uint8_t  *)dst.reg; break;

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