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Subject[PATCH] xen/x86: Adjust stack pointer in xen_sysexit
Date
After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
("x86/entry/32: Re-implement SYSENTER using the new C path"), the stack
frame that is passed to xen_sysexit is no longer a "standard" one (i.e.
it's not pt_regs).

We need to adjust it so that subsequent xen_iret can use it.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---

Alternatively, we could return 0 from do_fast_syscall_32() if paravirt_enabled()
is true since Xen PV guests will end up using xen_iret one way or the other. And
then we won't need xen_sysexit at all.

arch/x86/xen/xen-asm_32.S | 23 ++++++++++++++++-------
1 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
index fd92a64..c70ec37 100644
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -36,15 +36,24 @@ check_events:

/*
* We can't use sysexit directly, because we're not running in ring0.
- * But we can easily fake it up using iret. Assuming xen_sysexit is
- * jumped to with a standard stack frame, we can just strip it back to
- * a standard iret frame and use iret.
+ * But we can easily fake it up using iret.
+ * We came here from the opportunistic SYSEXIT path in entry_SYSENTER_32
+ * which left the stack looking like this:
+ * $__USER_DS
+ * %ecx
+ * eflags
+ * $__USER_CS
+ * %eip
+ * %eax
+ * %gs
+ * %fs
+ * %es
+ * %ds <-- %esp
+ *
+ * so we need to adjust it to look like a standard iret frame
*/
ENTRY(xen_sysexit)
- movl PT_EAX(%esp), %eax /* Shouldn't be necessary? */
- orl $X86_EFLAGS_IF, PT_EFLAGS(%esp)
- lea PT_EIP(%esp), %esp
-
+ add $5*4, %esp
jmp xen_iret
ENDPROC(xen_sysexit)

--
1.7.1


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