x86/paravirt: add sysret/sysexit pvops for returning to 32-bit compatibility userspace

In a 64-bit system, we need separate sysret/sysexit operations to
return to a 32-bit userspace.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citirx.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/ia32/ia32entry.S

@@ -61,6 +61,19 @@
 	CFI_UNDEFINED	r15
 	.endm
 
+#ifdef CONFIG_PARAVIRT
+ENTRY(native_usergs_sysret32)
+	swapgs
+	sysretl
+ENDPROC(native_usergs_sysret32)
+
+ENTRY(native_irq_enable_sysexit)
+	swapgs
+	sti
+	sysexit
+ENDPROC(native_irq_enable_sysexit)
+#endif
+
 /*
  * 32bit SYSENTER instruction entry.
  *
@@ -151,10 +164,7 @@ sysenter_do_call:
 	CFI_ADJUST_CFA_OFFSET -8
 	CFI_REGISTER rsp,rcx
 	TRACE_IRQS_ON
-	swapgs
-	sti		/* sti only takes effect after the next instruction */
-	/* sysexit */
-	.byte	0xf, 0x35
+	ENABLE_INTERRUPTS_SYSEXIT32
 
 sysenter_tracesys:
 	CFI_RESTORE_STATE
@@ -254,8 +264,7 @@ cstar_do_call:
 	TRACE_IRQS_ON
 	movl RSP-ARGOFFSET(%rsp),%esp
 	CFI_RESTORE rsp
-	swapgs
-	sysretl
+	USERGS_SYSRET32
 	
 cstar_tracesys:	
 	CFI_RESTORE_STATE