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SubjectRe: [tip:x86/hyperv] x86/hyperv: Enable PV qspinlock for Hyper-V
On 18-10-02 13:38:55, Juergen Gross wrote:
> > +static void hv_qlock_wait(u8 *byte, u8 val)
> > +{
> > + unsigned long msr_val;
> > +
> > + if (READ_ONCE(*byte) != val)
> > + return;
> > +
> > + /*
> > + * 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.
>
>
> Juergen

Thank you for the suggestion! That is a possible case. I will submit
a new version in soon.

BRs,
Yi Sun

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