[PATCH 4 of 5] xen: allow some cr4 updates

[Jeremy Fitzhardinge <jeremy@goop.org>]

The guest can legitimately change things like cr4.OSFXSR and
OSXMMEXCPT, so let it.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
 arch/x86/xen/enlighten.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -648,8 +648,10 @@
 
 static void xen_write_cr4(unsigned long cr4)
 {
-	/* Just ignore cr4 changes; Xen doesn't allow us to do
-	   anything anyway. */
+	cr4 &= ~X86_CR4_PGE;
+	cr4 &= ~X86_CR4_PSE;
+
+	native_write_cr4(cr4);
 }
 
 static unsigned long xen_read_cr3(void)