Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers

Jürgen Groß
2020-08-11T07:58:00Z

On 11.08.20 09:41, Peter Zijlstra wrote:
> On Fri, Aug 07, 2020 at 05:19:03PM +0200, Marco Elver wrote:
>
>> My hypothesis here is simply that kvm_wait() may be called in a place
>> where we get the same case I mentioned to Peter,
>>
>> raw_local_irq_save(); /* or other IRQs off without tracing */
>> ...
>> kvm_wait() /* IRQ state tracing gets confused */
>> ...
>> raw_local_irq_restore();
>>
>> and therefore, using raw variants in kvm_wait() works. It's also safe
>> because it doesn't call any other libraries that would result in corrupt
>
> Yes, this is definitely an issue.
>
> Tracing, we also musn't call into tracing when using raw_local_irq_*().
> Because then we re-intoduce this same issue all over again.
>
> Both halt() and safe_halt() are more paravirt calls, but given we're in
> a KVM paravirt call already, I suppose we can directly use native_*()
> here.
>
> Something like so then... I suppose, but then the Xen variants need TLC
> too.

Just to be sure I understand you correct:

You mean that xen_qlock_kick() and xen_qlock_wait() and all functions
called by those should gain the "notrace" attribute, right?

I am not sure why the kick variants need it, though. IMO those are
called only after the lock has been released, so they should be fine
without notrace.

And again: we shouldn't forget the Hyper-V variants.

Juergen