KVM: x86: retry non-page-table writing instructions

If the emulation is caused by #PF and it is non-page_table writing instruction,
it means the VM-EXIT is caused by shadow page protected, we can zap the shadow
page and retry this instruction directly

The idea is from Avi

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index a10950a..8547958 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3702,6 +3702,11 @@
 	return (rc != X86EMUL_CONTINUE) ? EMULATION_FAILED : EMULATION_OK;
 }
 
+bool x86_page_table_writing_insn(struct x86_emulate_ctxt *ctxt)
+{
+	return ctxt->d & PageTable;
+}
+
 static bool string_insn_completed(struct x86_emulate_ctxt *ctxt)
 {
 	/* The second termination condition only applies for REPE