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, 17 insertions, 1 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 568c6ccd7ae2..5d80d53eaff8 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1017,6 +1017,13 @@ ENTRY(kernel_thread_helper)
 ENDPROC(kernel_thread_helper)
 
 #ifdef CONFIG_XEN
+/* Xen doesn't set %esp to be precisely what the normal sysenter
+   entrypoint expects, so fix it up before using the normal path. */
+ENTRY(xen_sysenter_target)
+        RING0_INT_FRAME
+        addl $5*4, %esp         /* remove xen-provided frame */
+        jmp sysenter_past_esp
+
 ENTRY(xen_hypervisor_callback)
         CFI_STARTPROC
         pushl $0
@@ -1036,8 +1043,17 @@ ENTRY(xen_hypervisor_callback)
         jae  1f
 
         call xen_iret_crit_fixup
+        jmp  2f
+
+1:      cmpl $xen_sysexit_start_crit,%eax
+        jb   2f
+        cmpl $xen_sysexit_end_crit,%eax
+        jae  2f
+
+        jmp xen_sysexit_crit_fixup
 
-1:      mov %esp, %eax
+ENTRY(xen_do_upcall)
+2:      mov %esp, %eax
         call xen_evtchn_do_upcall
         jmp  ret_from_intr
         CFI_ENDPROC