linux-kernel - Re: [RFC PATCH v3 00/16] Core scheduling v3

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Message-ID: <20190828161641.GJ2369@hirez.programming.kicks-ass.net>
Date:   Wed, 28 Aug 2019 18:16:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        subhra.mazumdar@...cle.com, fweisbec@...il.com,
        keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3

On Wed, Aug 28, 2019 at 08:59:21AM -0700, Tim Chen wrote:
> On 8/27/19 2:50 PM, Peter Zijlstra wrote:
> > On Tue, Aug 27, 2019 at 10:14:17PM +0100, Matthew Garrett wrote:
> >> Apple have provided a sysctl that allows applications to indicate that 
> >> specific threads should make use of core isolation while allowing 
> >> the rest of the system to make use of SMT, and browsers (Safari, Firefox 
> >> and Chrome, at least) are now making use of this. Trying to do something 
> >> similar using cgroups seems a bit awkward. Would something like this be 
> >> reasonable? 
> > 
> > Sure; like I wrote earlier; I only did the cgroup thing because I was
> > lazy and it was the easiest interface to hack on in a hurry.
> > 
> > The rest of the ABI nonsense can 'trivially' be done later; if when we
> > decide to actually do this.
> > 
> > And given MDS, I'm still not entirely convinced it all makes sense. If
> > it were just L1TF, then yes, but now...
> > 
> 
> For MDS, core-scheduler does prevent thread to thread
> attack between user space threads running on sibling CPU threads.
> Yes, it doesn't prevent the user to kernel attack from sibling
> which will require additional mitigation measure. However, it does
> block a major attack vector for MDS if HT is enabled.

I'm not sure what your argument is; the dike has two holes; you plug
one, you still drown.