[patch V5 15/38] x86/entry: Change exit path of xen_failsafe_callback

Thomas Gleixner
2020-05-12T22:24:17Z

xen_failsafe_callback is invoked from XEN for two cases:

1. Fault while reloading DS, ES, FS or GS
2. Fault while executing IRET

#1 retries the IRET after XEN has fixed up the segments.
#2 injects a #GP which kills the task

For #1 there is no reason to go through the full exception return path
because the tasks TIF state is still the same. So just going straight to
the IRET path is good enough.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
---
arch/x86/entry/entry_32.S | 2 +-
arch/x86/entry/entry_64.S | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1352,7 +1352,7 @@ SYM_FUNC_START(xen_failsafe_callback)
5: pushl $-1 /* orig_ax = -1 => not a system call */
SAVE_ALL
ENCODE_FRAME_POINTER
- jmp ret_from_exception
+ jmp handle_exception_return

.section .fixup, "ax"
6: xorl %eax, %eax
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1175,7 +1175,7 @@ SYM_CODE_START(xen_failsafe_callback)
pushq $-1 /* orig_ax = -1 => not a system call */
PUSH_AND_CLEAR_REGS
ENCODE_FRAME_POINTER
- jmp error_exit
+ jmp error_return
SYM_CODE_END(xen_failsafe_callback)
#endif /* CONFIG_XEN_PV */