Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Tue, Sep 05, 2017 at 10:02:57AM -0400, Waiman Long wrote:
> On 09/05/2017 09:24 AM, Juergen Gross wrote:

> > +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> > +{
> > +   if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> > +           return false;
> > +
> 
> I think you can take the above if statement out as you has done test in
> native_pv_lock_init(). So the test will also be false here.

That does mean we'll run a test-and-set spinlock until paravirt patching
happens though. I prefer to not do that.

One important point.. we must not be holding any locks when we switch
over between the two locks. Back then I spend some time making sure that
didn't happen with the X86 feature flag muck.

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