From b9c113aaddcaca13df2468957f03cbb8614c0792 Mon Sep 17 00:00:00 2001
From: jhb <jhb@FreeBSD.org>
Date: Thu, 26 Jun 2014 19:19:06 +0000
Subject: MFC 264277: Handle single-byte reads from the bvmcons port (0x220) by
 returning 0xff.  Some guests may attempt to read from this port to identify
 psuedo-PNP ISA devices.  (The ie(4) driver in FreeBSD/i386 is one example.)

---
 usr.sbin/bhyve/consport.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/usr.sbin/bhyve/consport.c b/usr.sbin/bhyve/consport.c
index b9eb4ce..4074e95 100644
--- a/usr.sbin/bhyve/consport.c
+++ b/usr.sbin/bhyve/consport.c
@@ -110,6 +110,15 @@ console_handler(struct vmctx *ctx, int vcpu, int in, int port, int bytes,
 		return (0);
 	}
 
+	/*
+	 * Guests might probe this port to look for old ISA devices
+	 * using single-byte reads.  Return 0xff for those.
+	 */
+	if (bytes == 1 && in) {
+		*eax = 0xff;
+		return (0);
+	}
+
 	if (bytes != 4)
 		return (-1);
 
-- 
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