[095/151] xen: use iret for return from 64b kernel to 32b usermode

Greg KH
2009-12-17T04:27:28Z

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

commit 6aaf5d633bb6cead81b396d861d7bae4b9a0ba7e upstream.

If Xen wants to return to a 32b usermode with sysret it must use the
right form. When using VCGF_in_syscall to trigger this, it looks at
the code segment and does a 32b sysret if it is FLAT_USER_CS32.
However, this is different from __USER32_CS, so it fails to return
properly if we use the normal Linux segment.

So avoid the whole mess by dropping VCGF_in_syscall and simply use
plain iret to return to usermode.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/xen/xen-asm_64.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -96,7 +96,7 @@ ENTRY(xen_sysret32)
pushq $__USER32_CS
pushq %rcx

- pushq $VGCF_in_syscall
+ pushq $0
1: jmp hypercall_iret
ENDPATCH(xen_sysret32)
RELOC(xen_sysret32, 1b+1)
@@ -151,7 +151,7 @@ ENTRY(xen_syscall32_target)
ENTRY(xen_sysenter_target)
lea 16(%rsp), %rsp /* strip %rcx, %r11 */
mov $-ENOSYS, %rax
- pushq $VGCF_in_syscall
+ pushq $0
jmp hypercall_iret
ENDPROC(xen_syscall32_target)
ENDPROC(xen_sysenter_target)