speed up KVM by avoiding invalid guest state emulation

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/cstart.S b/cstart.S
index cef3950..938139c 100644
--- a/cstart.S
+++ b/cstart.S
@@ -5,6 +5,8 @@
 	xor %ax, %ax
 	mov %ax, %ds
 	mov %ax, %es
+	mov %ax, %fs
+	mov %ax, %gs
 	mov %ax, %ss
 	mov $0x7c00, %sp
 
@@ -18,6 +20,8 @@
 	mov $16, %ax
 	mov %ax, %ds
 	mov %ax, %es
+	mov %ax, %fs
+	mov %ax, %gs
 	mov %ax, %ss
 	ljmp $8, $0xffff0000