Re: [PATCH 3/3] arch/x86: Optionally flush L1D on context switch

[Singh, Balbir]

On Fri, 2020-04-03 at 00:11 +0200, Borislav Petkov wrote:
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> On Thu, Apr 02, 2020 at 05:24:01PM +1100, Balbir Singh wrote:
> > +int enable_l1d_flush_for_task(struct task_struct *tsk)
> > +{
> > +     struct page *page;
> > +     int ret = 0;
> > +
> > +     if (static_cpu_has(X86_FEATURE_FLUSH_L1D))
> > +             goto done;
> > +
> > +     page = READ_ONCE(l1d_flush_pages);
> > +     if (unlikely(!page)) {
> > +             mutex_lock(&l1d_flush_mutex);
> > +             if (!l1d_flush_pages) {
> > +                     l1d_flush_pages = alloc_l1d_flush_pages();
> > +                     if (!l1d_flush_pages)
> > +                             return -ENOMEM;
> 
> Do I see it correctly that you'll return here with l1d_flush_mutex still
> held?

Darn.. :(

I had goto done to release the mutex earlier, let me fix that :)

Thanks,
Balbir Singh

> 
> > +             }
> > +             mutex_unlock(&l1d_flush_mutex);
> > +     }
> > +     /* I don't think we need to worry about KSM */
> 
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