xen: jump to iret fixup

Use jmp rather than call for the iret fixup, so its consistent with
the sysexit fixup, and it simplifies the stack (which is already
complex).
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/entry_32.S

@@ -1042,8 +1042,7 @@ ENTRY(xen_hypervisor_callback)
 	cmpl $xen_iret_end_crit,%eax
 	jae  1f
 
-	call xen_iret_crit_fixup
-	jmp  2f
+	jmp  xen_iret_crit_fixup
 
 1:	cmpl $xen_sysexit_start_crit,%eax
 	jb   2f

arch/x86/xen/xen-asm.S

@@ -223,9 +223,7 @@ hyper_iret:
 	 ds		}  SAVE_ALL state
 	 eax		}
 	  :		:
-	 ebx		}
-	----------------
-	 return addr	 <- esp
+	 ebx		}<- esp
 	----------------
 
    In order to deliver the nested exception properly, we need to shift
@@ -240,10 +238,8 @@ hyper_iret:
    it's usermode state which we eventually need to restore.
  */
 ENTRY(xen_iret_crit_fixup)
-	/* offsets +4 for return address */
-
 	/*
-	   Paranoia: Make sure we're really coming from userspace.
+	   Paranoia: Make sure we're really coming from kernel space.
 	   One could imagine a case where userspace jumps into the
 	   critical range address, but just before the CPU delivers a GP,
 	   it decides to deliver an interrupt instead.  Unlikely?
@@ -252,32 +248,32 @@ ENTRY(xen_iret_crit_fixup)
 	   jump instruction itself, not the destination, but some virtual
 	   environments get this wrong.
 	 */
-	movl PT_CS+4(%esp), %ecx
+	movl PT_CS(%esp), %ecx
 	andl $SEGMENT_RPL_MASK, %ecx
 	cmpl $USER_RPL, %ecx
 	je 2f
 
-	lea PT_ORIG_EAX+4(%esp), %esi
-	lea PT_EFLAGS+4(%esp), %edi
+	lea PT_ORIG_EAX(%esp), %esi
+	lea PT_EFLAGS(%esp), %edi
 
 	/* If eip is before iret_restore_end then stack
 	   hasn't been restored yet. */
 	cmp $iret_restore_end, %eax
 	jae 1f
 
-	movl 0+4(%edi),%eax		/* copy EAX */
-	movl %eax, PT_EAX+4(%esp)
+	movl 0+4(%edi),%eax		/* copy EAX (just above top of frame) */
+	movl %eax, PT_EAX(%esp)
 
 	lea ESP_OFFSET(%edi),%edi	/* move dest up over saved regs */
 
 	/* set up the copy */
 1:	std
-	mov $(PT_EIP+4) / 4, %ecx	/* copy ret+saved regs up to orig_eax */
+	mov $PT_EIP / 4, %ecx		/* saved regs up to orig_eax */
 	rep movsl
 	cld
 
 	lea 4(%edi),%esp		/* point esp to new frame */
-2:	ret
+2:	jmp xen_do_upcall
 
 
 ENTRY(xen_sysexit)