linux-kernel - Re: [RFC 00/60] Coscheduling for Linux

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Message-ID: <859c89b3-f43f-c3c7-3064-6bccb3ee65f8@redhat.com>
Date:   Thu, 4 Oct 2018 09:29:29 -0400
From:   Jon Masters <jcm@...hat.com>
To:     Jan H. Schönherr <jschoenh@...zon.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/60] Coscheduling for Linux

On 9/7/18 5:39 PM, Jan H. Schönherr wrote:

> The collective context switch from one coscheduled set of tasks to another
> -- while fast -- is not atomic. If a use-case needs the absolute guarantee
> that all tasks of the previous set have stopped executing before any task
> of the next set starts executing, an additional hand-shake/barrier needs to
> be added.

In case nobody else brought it up yet, you're going to need a handshake
to strengthen protection against L1TF attacks. Otherwise, there's still
a small window where an attack can occur during the reschedule. Perhaps
one could then cause this to happen artificially by repeatedly have a VM
do some kind of pause/mwait type operation that might do a reschedule.

Jon.

-- 
Computer Architect | Sent with my Fedora powered laptop