Re: [PATCH v2 01/24] x86/xen: Mark cpu_bringup_and_idle() as dead_end_function

[Miroslav Benes]

On Thu, 24 Jun 2021, Peter Zijlstra wrote:

> 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@xxxxxxxxxxxxx>

Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>

M