Re: rowhammer protection [was Re: Getting interrupt every million cache misses]

[Pavel Machek]

On Fri 2016-10-28 09:07:01, Ingo Molnar wrote:
> 
> * Pavel Machek <pavel@xxxxxx> wrote:
> 
> > +static void rh_overflow(struct perf_event *event, struct perf_sample_data *data, struct pt_regs *regs)
> > +{
> > +	u64 *ts = this_cpu_ptr(&rh_timestamp); /* this is NMI context */
> > +	u64 now = ktime_get_mono_fast_ns();
> > +	s64 delta = now - *ts;
> > +
> > +	*ts = now;
> > +
> > +	/* FIXME msec per usec, reverse logic? */
> > +	if (delta < 64 * NSEC_PER_MSEC)
> > +		mdelay(56);
> > +}
> 
> I'd suggest making the absolute delay sysctl tunable, because 'wait 56 msecs' is 
> very magic, and do we know it 100% that 56 msecs is what is needed
> everywhere?

I agree this needs to be tunable (and with the other suggestions). But
this is actually not the most important tunable: the detection
threshold (rh_attr.sample_period) should be way more important.

And yes, this will all need to be tunable, somehow. But lets verify
that this works, first :-).

Thanks and best regards,
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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