x86: use __KERNEL_DS as SS when returning to a kernel thread

This is needed when the kernel is running on RING3, such as under Xen.
x86_64 has a weird feature that makes it #GP on iret when SS is a null
descriptor.

This need to be tested on bare metal to make sure it doesn't cause any
problems. AMD specs say SS is always ignored (except on iret?).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.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>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index ff15ab552280d348602a4e6480a9262ced50e1f4..6d1101469e9757f72311fa3230043dd5534433f7 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -104,7 +104,7 @@ ENTRY(native_irq_enable_syscall_ret)
        .macro FAKE_STACK_FRAME child_rip
        /* push in order ss, rsp, eflags, cs, rip */
        xorl %eax, %eax
-       pushq %rax /* ss */
+       pushq $__KERNEL_DS /* ss */
        CFI_ADJUST_CFA_OFFSET   8
        /*CFI_REL_OFFSET        ss,0*/
        pushq %rax /* rsp */