[PATCH 4.1 63/65] kpti: Disable when running under Xen PV

[Pavel Tatashin]

From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Very very partial backport from aa8c6248f8c75 where
there is a check to see if this is an Xen PV guest - and
if so disable it.

The reason is that the PV ABI would require a major
overhaul to be Meltdown resistent.

Instead there are mitigations (PV in HVM) which are far more
suitable.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/mm/kaiser.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
index 50783ad4861d..05fb616c9e2a 100644
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -10,6 +10,7 @@
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
+#include <xen/xen.h>
 
 #include <asm/kaiser.h>
 #include <asm/tlbflush.h>	/* to verify its kaiser declarations */
@@ -264,6 +265,9 @@ void __init kaiser_check_boottime_disable(void)
 	char arg[5];
 	int ret;
 
+	if (xen_pv_domain())
+		goto disable;
+
 	ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
 	if (ret > 0) {
 		if (!strncmp(arg, "on", 2))
-- 
2.16.2