Re: [PATCH 1/2] x86/entry/64: Do not clear %rbx under Xen
From: M. Vefa Bicakci
Date: Sat Jul 21 2018 - 19:19:03 EST
On 07/21/2018 05:19 PM, Boris Ostrovsky wrote:
On 07/21/2018 03:49 PM, M. Vefa Bicakci wrote:
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index c7449f377a77..96e8ff34129e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1129,7 +1129,7 @@ ENTRY(xen_failsafe_callback)
addq $0x30, %rsp
UNWIND_HINT_IRET_REGS
pushq $-1 /* orig_ax = -1 => not a system call */
- PUSH_AND_CLEAR_REGS
+ PUSH_AND_CLEAR_REGS clear_rbx=0
Do we need this at all? We are returning from the hypervisor here.
-boris
ENCODE_FRAME_POINTER
jmp error_exit
END(xen_failsafe_callback)
Hello Boris,
If you are referring to the PUSH_AND_CLEAR_REGS macro itself, I am not sure;
however, not clearing the RBX register seemed to resolve the issues mentioned
in the commit message for me. Given Andy's comment though, I believe that the
approach in this patch may not be correct.
Thank you,
Vefa