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

[Jürgen Groß]

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