On Tue, 2 Oct 2018, Juergen Gross wrote:
> Sorry for noticing this only now, but I have been fighting with
> Xen PV qspinlocks last weekend:
>
> > + /*
> > + * Read HV_X64_MSR_GUEST_IDLE MSR can trigger the guest's
> > + * transition to the idle power state which can be exited
> > + * by an IPI even if IF flag is disabled.
> > + */
>
> What if interrupts are enabled? Won't a kick happening here just
> interrupt and then the following rdmsr result in a hang?
>
> I believe the correct way would be to:
>
> - disable interrupts before above READ_ONCE() and restore them
> after the rdmsrl()
>
> - return early if in_nmi()
>
> similar as the kvm specific variant is doing it.
Interesting question. I zapped the last commit for now until this is
clarified.
Thanks,
tglx
