From: Jeremy Fitzhardinge <jeremy@goop.org>
Date: Wed, 25 Jun 2008 04:19:25 +0000 (-0400)
Subject: x86: use __KERNEL_DS as SS when returning to a kernel thread
X-Git-Tag: v2.6.27-rc1~1106^2~127
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e04e0a630d8b5c621b3a8e70ff20db737d3a5728;p=linux-2.6

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 ff15ab5522..6d1101469e 100644
--- 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 */