On Wed, 2018-01-24 at 13:49 +0000, Andrew Cooper wrote: > On 24/01/18 13:34, Woodhouse, David wrote: > > I am loath to suggest *more* tweakables, but given the IBPB cost is > > there any merit in having a mode which does it only if the *domain* is > > different, regardless of vcpu_id? > > This would only be a win if you were regularly cross-scheduling vcpus > from the same domain, which case you've probably other issues to be > worried about.
Of course. If the guest *knows* about HT siblings that kind of implies you've told it about the topology and thus you're pinning vCPU. I don't think there *is* a world in which what I said makes sense. > > > > If a given domain is running on HT siblings, it ought to be doing its > > own mitigation — setting STIBP for userspace if it wants, ensuring its > > own kernel is safe by having IBRS set or using retpoline, etc. > ~Andrew > > [1] Is this trying to be a subtle hint? Heh, no. When I get to that bit, and the *reasons* we do that, it'll be far from subtle. But as with so many other things, NOT THIS WEEK :)
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