[PATCH 4.18 141/235] x86/EISA: Dont probe EISA bus for Xen PV guests

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

commit 6a92b11169a65b3f8cc512c75a252cbd0d096ba0 upstream.

For unprivileged Xen PV guests this is normal memory and ioremap will
not be able to properly map it.

While at it, since ioremap may return NULL, add a test for pointer's
validity.

Reported-by: Andy Smith <andy@xxxxxxxxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: hpa@xxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: jgross@xxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20180911195538.23289-1-boris.ostrovsky@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/kernel/eisa.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/eisa.c
+++ b/arch/x86/kernel/eisa.c
@@ -7,11 +7,17 @@
 #include <linux/eisa.h>
 #include <linux/io.h>
 
+#include <xen/xen.h>
+
 static __init int eisa_bus_probe(void)
 {
-	void __iomem *p = ioremap(0x0FFFD9, 4);
+	void __iomem *p;
+
+	if (xen_pv_domain() && !xen_initial_domain())
+		return 0;
 
-	if (readl(p) == 'E' + ('I'<<8) + ('S'<<16) + ('A'<<24))
+	p = ioremap(0x0FFFD9, 4);
+	if (p && readl(p) == 'E' + ('I' << 8) + ('S' << 16) + ('A' << 24))
 		EISA_bus = 1;
 	iounmap(p);
 	return 0;