linux-kernel - Re: [Problem] Cache line starvation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180928090521.mj5elgqnla6qcz2r@linutronix.de>
Date:   Fri, 28 Sep 2018 11:05:22 +0200
From:   Kurt Kanzenbach <kurt.kanzenbach@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Will Deacon <will.deacon@....com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Daniel Wagner <daniel.wagner@...mens.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [Problem] Cache line starvation

Hi Thomas,

On Thu, Sep 27, 2018 at 04:47:47PM +0200, Thomas Gleixner wrote:
> On Thu, 27 Sep 2018, Kurt Kanzenbach wrote:
> > On Thu, Sep 27, 2018 at 04:25:47PM +0200, Kurt Kanzenbach wrote:
> > > However, the issue still triggers fine. With stress-ng we're able to
> > > generate latency in millisecond range. The only workaround we've found
> > > so far is to add a "delay" in cpu_relax().
> >
> > It might interesting for you, how we added the delay. We've used:
> >
> > static inline void cpu_relax(void)
> > {
> > 	volatile int i = 0;
> >
> > 	asm volatile("yield" ::: "memory");
> > 	while (i++ <= 1000);
> > }
> >
> > Of course it's not efficient, but it works.
>
> I wonder if it's just the store on the stack which makes it work. I've seen
> that when instrumenting x86. When the careful instrumentation just stayed
> in registers it failed. Once it was too much and stack got involved it
> vanished away.

I've performed more tests: Adding a store to a global variable just
before calling cpu_relax() doesn't help. Furthermore, adding up to 20
yield instructions (just like you did on x86) didn't work either.

Thanks,
Kurt