xen: support sysenter/sysexit if hypervisor does

64-bit Xen supports sysenter for 32-bit guests, so support its
use.  (sysenter is faster than int $0x80 in 32-on-64.)

sysexit is still not supported, so we fake it up using iret.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 1 insertions, 2 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 36f36e6b0874..943684566ebe 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -155,7 +155,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
         if (*ax == 1)
                 maskedx = ~((1 << X86_FEATURE_APIC) |  /* disable APIC */
                             (1 << X86_FEATURE_ACPI) |  /* disable ACPI */
-                            (1 << X86_FEATURE_SEP)  |  /* disable SEP */
                             (1 << X86_FEATURE_ACC));   /* thermal monitoring */
 
         asm(XEN_EMULATE_PREFIX "cpuid"
@@ -994,7 +993,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initdata = {
         .read_pmc = native_read_pmc,
 
         .iret = xen_iret,
-        .irq_enable_syscall_ret = NULL,  /* never called */
+        .irq_enable_syscall_ret = xen_sysexit,
 
         .load_tr_desc = paravirt_nop,
         .set_ldt = xen_set_ldt,