Date: Thu, 27 Oct 2016 11:15:43 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: acme@redhat.com, kernel list <linux-kernel@vger.kernel.org>,
        mingo@redhat.com, alexander.shishkin@linux.intel.com
Subject: Re: Getting interrupt every million cache misses
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 <20161027084637.GA19469@amd>
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On Thu, Oct 27, 2016 at 10:46:38AM +0200, Pavel Machek wrote:

> And actually, printk() is not needed, udelay(50msec) is. Reason is,
> that DRAM becomes unreliable if about milion cache misses happen in
> under 64msec -- so I'd like to slow the system down in such cases to
> prevent bug from biting me.
> 
> (Details are here
> https://googleprojectzero.blogspot.cz/2015/03/exploiting-dram-rowhammer-bug-to-gain.html
> ). Bug is exploitable to get local root; it is also exploitable to
> gain local code execution from javascript... so it is rather severe.

Cute, a rowhammer defence.

So we can do in-kernel perf events too, see for example
kernel/watchdog.c:wd_hw_attr and its users.

I suppose you want PERF_COUNT_HW_CACHE_MISSES as config, although
depending on platform you could use better (u-arch specific) events.