From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Wed, 25 Nov 2009 21:15:38 +0000 (-0800)
Subject: xen: use iret for return from 64b kernel to 32b usermode
X-Git-Tag: firefly_0821_release~11625^2~540
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ebe5f3b81f1d3677882b5b1c382321096c7d1851;p=firefly-linux-kernel-4.4.55.git

xen: use iret for return from 64b kernel to 32b usermode

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>
---

diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index 02f496a8dbaa..53adefda4275 100644
--- 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)