Messages in this thread |  | | Subject | Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU) | From | David Woodhouse <> | Date | Tue, 21 Aug 2018 10:57:03 +0100 |
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On Mon, 2018-08-20 at 15:27 -0700, Linus Torvalds wrote: > On Mon, Aug 20, 2018 at 3:02 PM Woodhouse, David <dwmw@amazon.co.uk> wrote: > > > > It's the *kernel* we don't want being able to access those pages, > > because of the multitude of unfixable cache load gadgets. > > Ahh. > > I guess the proof is in the pudding. Did somebody try to forward-port > that patch set and see what the performance is like?
I hadn't actually seen the XPFO patch set before; we're going to take a serious look.
Of course, this is only really something that a select few people (with quite a lot of machines) would turn on. And they might be willing to tolerate a significant performance cost if the alternative way to be safe is to disable hyperthreading entirely — which is Intel's best recommendation so far, it seems.
Another alternative... I'm told POWER8 does an interesting thing with hyperthreading and gang scheduling for KVM. The host kernel doesn't actually *see* the hyperthreads at all, and KVM just launches the full set of siblings when it enters a guest, and gathers them again when any of them exits. That's definitely worth investigating as an option for x86, too. [unhandled content-type:application/x-pkcs7-signature] |  |