linux-kernel - Re: [RFC PATCH v7 17/23] kernel/entry: Add support for core-wide protection of kernel-mode

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Message-ID: <9471f752-1a30-d46f-be75-d3d433980385@linux.microsoft.com>
Date:   Thu, 3 Sep 2020 07:05:25 -0400
From:   Vineeth Pillai <viremana@...ux.microsoft.com>
To:     Joel Fernandes <joel@...lfernandes.org>,
        Dario Faggioli <dfaggioli@...e.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Dhaval Giani <dhaval.giani@...cle.com>,
        Chris Hyser <chris.hyser@...cle.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Agata Gruza <agata.gruza@...el.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
        graf@...zon.com, konrad.wilk@...cle.com,
        Steven Rostedt <rostedt@...dmis.org>,
        Patrick Bellasi <derkling@...gle.com>,
        benbjiang(蒋彪) <benbjiang@...cent.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Tim Chen <tim.c.chen@...el.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [RFC PATCH v7 17/23] kernel/entry: Add support for core-wide
 protection of kernel-mode



On 9/3/20 12:34 AM, Joel Fernandes wrote:
>>
>> Indeed! For at least two reasons, IMO:
>>
>> 1) what Thomas is saying already. I.e., even on a CPU which has HT but
>> is not affected by any of the (known!) speculation issues, one may want
>> to use Core Scheduling _as_a_feature_. For instance, for avoiding
>> threads from different processes, or vCPUs from different VMs, sharing
>> cores (e.g., for better managing their behavior/performance, or for
>> improved fairness of billing/accounting). And in this case, this
>> mechanism for protecting the kernel from the userspace on the other
>> thread may not be necessary or interesting;
> Agreed. So then I should really make this configurable and behind a
> sysctl then. I'll do that.
We already have the patch to wrap this feature in a build time and
boot time option:
https://lwn.net/ml/linux-kernel/9cd9abad06ad8c3f35228afd07c74c7d9533c412.1598643276.git.jdesfossez@digitalocean.com/

I could not get to a safe way to make it a runtime tunable at the time
of posting this series, but I think it should also be possible.

Thanks,
Vineeth