From: Anthony Liguori <aliguori@amazon.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: KVM L1TF options
Date: Mon, 2 Jul 2018 15:41:28 -0700 [thread overview]
Message-ID: <cig332tvph1crr.fsf@u44850075a5a8574dc8a1.ant.amazon.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1807030013000.1590@nanos.tec.linutronix.de>
speck for Thomas Gleixner <speck@linutronix.de> writes:
> On Mon, 2 Jul 2018, speck for Anthony Liguori wrote:
> > speck for Alexander Graf <speck@linutronix.de> writes:
> > > 2) Gang scheduling for vcpus, disallow non-kvm processes to run with kvm
> > >
> > > This seems to be quite tricky to get right from what I gather. I
> > > remember IBM had similar approaches for HV KVM on PowerPC initially, but
> > > eventually went with SMT1 on the host and SMTx in the guest, with KVM
> > > doing the ganging.
> >
> > There are at least a couple implementations of this already but my
> > understanding is that mingo/tglx have pushed back on doing this.
>
> You forgot Linus :)
>
> For my part I pushed back on this being the stuff which magically solves
> all problems and concentrating on it _before_ having the most obvious
> mitigation in place. I didn't want to end up in a situation where the mess
> goes public and we have our pants down (again).
>
> Aisde of that I really want to see something which is fully functional and
> does not immediately cause gastric ulcer when looking at it. What I've seen
> so far is horrible proof of concept hackery full of tinkering in regular
> fast paths, obvious bugs, interesting assumptions and suitable for a subset
> of workloads.
>
> I surely can see it work for particular workloads where the CPU resources
> are partitioned and exits are really rare, but nobody so far explained how
> this could ever work for general workloads with overcommitment, lots of
> single VCPU guests, vmexit heavy scenarios etc. without creating a horrible
> overhead, wreckaging load balancing and other subtle issues.
>
> I'm open for being educated on that, but I definitely won't put my money on
> it.
>
> > Regardless, we plan on posting an implementation once the embargo lifts.
>
> If you have stuff ready, feel free to post it here once the minimal
> mitigation has been settled in the next couple of days.
I think we're close enough to send. I'll ask the engineer to send it
out here.
Regards,
Anthony Liguori
>
> Thanks,
>
> tglx
next prev parent reply other threads:[~2018-07-02 22:41 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-02 21:41 [MODERATED] KVM L1TF options Alexander Graf
2018-07-02 21:44 ` [MODERATED] " Dave Hansen
2018-07-02 22:02 ` Anthony Liguori
2018-07-02 22:28 ` [MODERATED] Re: ***UNCHECKED*** " Alexander Graf
2018-07-02 22:33 ` Thomas Gleixner
2018-07-02 22:41 ` Anthony Liguori [this message]
2018-07-03 8:36 ` [MODERATED] " Paolo Bonzini
2018-07-03 12:50 ` [MODERATED] Re: ***UNCHECKED*** " Alexander Graf
2018-07-04 14:33 ` [MODERATED] " Jiri Kosina
2018-07-04 14:51 ` [MODERATED] Re: ***UNCHECKED*** " Alexander Graf
2018-07-05 19:22 ` [MODERATED] " Jon Masters
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