On Mon, 2018-08-20 at 15:27 -0700, Linus Torvalds wrote: > On Mon, Aug 20, 2018 at 3:02 PM Woodhouse, David <dwmw@xxxxxxxxxxxx> 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.
Attachment:
smime.p7s
Description: S/MIME cryptographic signature
