x86_emulate: Emulate CLFLUSH instruction

We recently found that FreeBSD 8.0 guest failed to install and boot on
Xen. The reason was that FreeBSD detected clflush feature and invoked
this instruction to flush MMIO space. This caused a page fault; but
x86_emulate.c failed to emulate this instruction (not supported). As a
result, a page fault was detected inside FreeBSD. A similar issue was
reported earlier.

http://lists.xensource.com/archives/html/xen-devel/2010-03/msg00362.html

From: Wei Huang <wei.huang2@amd.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 15 insertions, 1 deletions

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 3449f21eab..51e199adbc 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -227,7 +227,8 @@ static uint8_t twobyte_table[256] = {
     DstMem|SrcReg|ModRM, DstMem|SrcReg|ModRM, 0, 0,
     /* 0xA8 - 0xAF */
     ImplicitOps, ImplicitOps, 0, DstBitBase|SrcReg|ModRM,
-    DstMem|SrcReg|ModRM, DstMem|SrcReg|ModRM, 0, DstReg|SrcMem|ModRM,
+    DstMem|SrcReg|ModRM, DstMem|SrcReg|ModRM,
+    ImplicitOps|ModRM, DstReg|SrcMem|ModRM,
     /* 0xB0 - 0xB7 */
     ByteOp|DstMem|SrcReg|ModRM, DstMem|SrcReg|ModRM,
     DstReg|SrcMem|ModRM|Mov, DstBitBase|SrcReg|ModRM,
@@ -4008,6 +4009,19 @@ x86_emulate(
         emulate_2op_SrcV_nobyte("bts", src, dst, _regs.eflags);
         break;
 
+    case 0xae: /* Grp15 */
+        switch ( modrm_reg & 7 )
+        {
+        case 7: /* clflush */
+            fail_if(ops->wbinvd == NULL);
+            if ( (rc = ops->wbinvd(ctxt)) != 0 )
+                goto done;
+            break;
+        default:
+            goto cannot_emulate;
+        }
+        break;
+
     case 0xaf: /* imul */
         _regs.eflags &= ~(EFLG_OF|EFLG_CF);
         switch ( dst.bytes )