Patch-mainline: v5.16-rc1
Git-commit: 9af9dcf11bda3e2c0e24c1acaacb8685ad974e93
References: git-fixes
From: Peter Zijlstra <peterz@infradead.org>
Date: Thu, 24 Jun 2021 11:41:00 +0200
Subject: [PATCH] x86/xen: Mark cpu_bringup_and_idle() as dead_end_function

The asm_cpu_bringup_and_idle() function is required to push the return
value on the stack in order to make ORC happy, but the only reason
objtool doesn't complain is because of a happy accident.

The thing is that asm_cpu_bringup_and_idle() doesn't return, so
validate_branch() never terminates and falls through to the next
function, which in the normal case is the hypercall_page. And that, as
it happens, is 4095 NOPs and a RET.

Make asm_cpu_bringup_and_idle() terminate on it's own, by making the
function it calls as a dead-end. This way we no longer rely on what
code happens to come after.

Fixes: c3881eb58d56 ("x86/xen: Make the secondary CPU idle tasks reliable")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lore.kernel.org/r/20210624095147.693801717@infradead.org
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 tools/objtool/check.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e5947fbb9e7a..0e3981d91afc 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -161,6 +161,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"usercopy_abort",
 		"machine_real_restart",
 		"rewind_stack_do_exit",
+		"cpu_bringup_and_idle",
 	};
 
 	if (!func)
-- 
2.26.2