Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Andy Lutomirski
2018-11-29T17:31:10Z

> On Nov 29, 2018, at 9:07 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Nov 29, 2018 at 09:02:23AM -0800, Andy Lutomirski wrote:
>>> On Nov 29, 2018, at 8:50 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>>> So no. Do *not* try to change %rsp on the stack in the bp handler.
>>> Instead, I'd suggest:
>>>
>>> - just restart the instruction (with the suggested "ptregs->rip --")
>>>
>>> - to avoid any "oh, we're not making progress" issues, just fix the
>>> instruction yourself to be the right call, by looking it up in the
>>> "what needs to be fixed" tables.
>>>
>>> No?
>
>> Or do you think we can avoid the IPI while the int3 is there?
>
> I'm thinking Linus is suggesting the #BP handler does the text write too
> (as a competing store) and then sync_core() and restarts.
>
> But I think that is broken, because then there is no telling what the
> other CPUs will observe.

Does anyone know what the actual hardware semantics are? The SDM is not particularly informative unless I looked at the wrong section.