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
I created a patch which enables clflush emulation. I have verified that
this patch solves FreeBSD issue. This patch returns immediately without
doing anything. Note that we don't have to intercept clflush in SVM. So
the only time we have page_fault for clflush instruction is when guest
VM flushes MMIO space. In this case, do we need to send this command
over to QEMU? I didn't do it in this patch anyway.
Best,
-Wei
diff -r 12a610b600b0 xen/arch/x86/x86_emulate/x86_emulate.c
--- a/xen/arch/x86/x86_emulate/x86_emulate.c Wed Apr 14 11:50:00 2010 -0500
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c Wed Apr 14 16:11:36 2010 -0500
@@ -227,7 +227,8 @@
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, DstMem|SrcReg|ModRM,
+ DstReg|SrcMem|ModRM,
/* 0xB0 - 0xB7 */
ByteOp|DstMem|SrcReg|ModRM, DstMem|SrcReg|ModRM,
DstReg|SrcMem|ModRM|Mov, DstBitBase|SrcReg|ModRM,
@@ -3948,6 +3949,11 @@
src.val = x86_seg_gs;
goto pop_seg;
+ case 0xae: /* clflush mem8 */
+ /* we don't need to do anything here */
+ rc = X86EMUL_OKAY;
+ break;
+
case 0xb0 ... 0xb1: /* cmpxchg */
/* Save real source value, then compare EAX against destination. */
src.orig_val = src.val;
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
Home