From c51b496e0b2f94c0dd2db6c0ede4db0b6c40a8b2 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sun, 17 Mar 2019 18:31:48 +0000
Subject: [PATCH] i386: improve detection of the fast page fault assist.

In particular, check that we are assisting the page fault from kernel mode.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
---
 sys/i386/i386/exception.s | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sys/i386/i386/exception.s b/sys/i386/i386/exception.s
index 2ee5032312a9..a4b57876be95 100644
--- a/sys/i386/i386/exception.s
+++ b/sys/i386/i386/exception.s
@@ -131,6 +131,10 @@ IDTVEC(prot)
 	pushl	$T_PROTFLT
 	jmp	irettraps
 IDTVEC(page)
+	testl	$PSL_VM, TF_EFLAGS-TF_ERR(%esp)
+	jnz	1f
+	testb	$SEL_RPL_MASK, TF_CS-TF_ERR(%esp)
+	jnz	1f
 	cmpl	$PMAP_TRM_MIN_ADDRESS, TF_EIP-TF_ERR(%esp)
 	jb	1f
 	movl	%ebx, %cr3