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>

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 3449f21eabcab7acc0c968e53de02973c9b8494c..51e199adbc55bd0a595e1089b99ad9ed20a002a1 100644 (file)
--- 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 )