Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <cover.1583332764.git.vpillai@digitalocean.com>
 <20200510234652.249917-1-joel@joelfernandes.org> <20200511134921.GC2940@hirez.programming.kicks-ass.net>
In-Reply-To: <20200511134921.GC2940@hirez.programming.kicks-ass.net>
From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Mon, 11 May 2020 10:54:54 -0400
Message-ID: <CAEXW_YQvVvNS5e89YQX7GALxPUXoymuZ_pDN+5iaAj_yiN3abg@mail.gmail.com>
Subject: Re: [PATCH RFC] Add support for core-wide protection of IRQ and softirq
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Vineeth Pillai <vpillai@digitalocean.com>,
        Allison Randal <allison@lohutok.net>,
        Armijn Hemel <armijn@tjaldur.nl>,
        Ben Segall <bsegall@google.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Mel Gorman <mgorman@suse.de>, Muchun Song <smuchun@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vincent Guittot <vincent.guittot@linaro.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, May 11, 2020 at 9:49 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Sun, May 10, 2020 at 07:46:52PM -0400, Joel Fernandes (Google) wrote:
> > With current core scheduling patchset, non-threaded IRQ and softirq
> > victims can leak data from its hyperthread to a sibling hyperthread
> > running an attacker.
> >
> > For MDS, it is possible for the IRQ and softirq handlers to leak data to
> > either host or guest attackers. For L1TF, it is possible to leak to
> > guest attackers. There is no possible mitigation involving flushing of
> > buffers to avoid this since the execution of attacker and victims happen
> > concurrently on 2 or more HTs.
> >
> > The solution in this patch is to monitor the outer-most core-wide
> > irq_enter() and irq_exit() executed by any sibling. In between these
> > two, we mark the core to be in a special core-wide IRQ state.
>
> Another possible option is force_irqthreads :-) That would cure it
> nicely.

Yes true, it was definitely my "plan B" at one point if this patch
showed any regression. Lastly, people not doing force_irqthreads would
still leave a hole open and it'd be nice to solve it by "default" than
depending on user/sysadmin configuration (same argument against
interrupt affinities, it is another knob for the sysadmin/designer to
configure correctly, Another argument being not all interrupts can be
threaded / affinitized).

Thanks in advance for reviewing the patch,

 - Joel