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 19:20:58 +0000
Message-ID: <4F6CCD1A.4090505@citrix.com>
References: <20120323114425.07bd6db7@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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Patch attached.

Not tested, but seems logically correct.

@Mukesh: Do you mind testing please?

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


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# HG changeset patch
# Parent 0ecb8ffe61b2ffff4331fcf49487c956ccb297a0
x86_emulate: Force #UD if lock prefix used with NOP instruction.

DTRACE uses 0xF0 0x90 0x90 0x90 0x90 (LOCK NOP NOP NOP NOP) to try and recieve a
#UD, but currently get GPF instead.

Fix x86_emulate, as #UD is the correct exception in this case.

Reported-by: Mukesh Rathor <mukesh.rathor@oracle.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

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
@@ -2255,6 +2255,7 @@ x86_emulate(
         break;
 
     case 0x90: /* nop / xchg %%r8,%%rax */
+        generate_exception_if(lock_prefix, EXC_UD, -1);
         if ( !(rex_prefix & 1) )
             break; /* nop */
 

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