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, 21 insertions, 0 deletions

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 2341492bf7a0..82517e4a752a 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -16,6 +16,7 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
 
+#include <xen/interface/callback.h>
 #include <xen/interface/physdev.h>
 #include <xen/features.h>
 
@@ -68,6 +69,24 @@ static void __init fiddle_vdso(void)
         *mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;
 }
 
+void xen_enable_sysenter(void)
+{
+        int cpu = smp_processor_id();
+        extern void xen_sysenter_target(void);
+        /* Mask events on entry, even though they get enabled immediately */
+        static struct callback_register sysenter = {
+                .type = CALLBACKTYPE_sysenter,
+                .address = { __KERNEL_CS, (unsigned long)xen_sysenter_target },
+                .flags = CALLBACKF_mask_events,
+        };
+
+        if (!boot_cpu_has(X86_FEATURE_SEP) ||
+            HYPERVISOR_callback_op(CALLBACKOP_register, &sysenter) != 0) {
+                clear_cpu_cap(&cpu_data(cpu), X86_FEATURE_SEP);
+                clear_cpu_cap(&boot_cpu_data, X86_FEATURE_SEP);
+        }
+}
+
 void __init xen_arch_setup(void)
 {
         struct physdev_set_iopl set_iopl;
@@ -82,6 +101,8 @@ void __init xen_arch_setup(void)
         HYPERVISOR_set_callbacks(__KERNEL_CS, (unsigned long)xen_hypervisor_callback,
                                  __KERNEL_CS, (unsigned long)xen_failsafe_callback);
 
+        xen_enable_sysenter();
+
         set_iopl.iopl = 1;
         rc = HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
         if (rc != 0)