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

[Ingo Molnar <mingo@kernel.org>]

* Pavel Machek <pavel@ucw.cz> 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?

Plus I'd also suggest exposing an 'NMI rowhammer delay count' in /proc/interrupts, 
to make it easier to debug this. (Perhaps only show the line if the count is 
nonzero.)

Finally, could we please also add a sysctl and Kconfig that allows this feature to 
be turned on/off, with the default bootup value determined by the Kconfig value 
(i.e. by the distribution)? Similar to CONFIG_SECURITY_SELINUX_BOOTPARAM_VALUE.

Thanks,

	Ingo