Messages in this thread | | | Subject | Re: [PATCH] KVM: VMX: Enable Notify VM exit | From | Tao Xu <> | Date | Tue, 3 Nov 2020 13:35:08 +0800 |
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On 11/3/20 1:31 AM, Sean Christopherson wrote: > On Mon, Nov 02, 2020 at 08:43:30AM -0800, Andy Lutomirski wrote: >> On Sun, Nov 1, 2020 at 10:14 PM Tao Xu <tao3.xu@intel.com> wrote: >>> 2. Another patch to disable interception of #DB and #AC when notify >>> VM-Exiting is enabled. >> >> Whoa there. >> >> A VM control that says "hey, CPU, if you messed up and livelocked for >> a long time, please break out of the loop" is not a substitute for >> fixing the livelocks. So I don't think you get do disable >> interception of #DB and #AC. > > I think that can be incorporated into a module param, i.e. let the platform > owner decide which tool(s) they want to use to mitigate the legacy architecture > flaws. > >> I also think you should print a loud warning > > I'm not so sure on this one, e.g. userspace could just spin up a new instance > if its malicious guest and spam the kernel log. > >> and have some intelligent handling when this new exit triggers. > > We discussed something similar in the context of the new bus lock VM-Exit. I > don't know that it makes sense to try and add intelligence into the kernel. > In many use cases, e.g. clouds, the userspace VMM is trusted (inasmuch as > userspace can be trusted), while the guest is completely untrusted. Reporting > the error to userspace and letting the userspace stack take action is likely > preferable to doing something fancy in the kernel. > > > Tao, this patch should probably be tagged RFC, at least until we can experiment > with the threshold on real silicon. KVM and kernel behavior may depend on the > accuracy of detecting actual attacks, e.g. if we can set a threshold that has > zero false negatives and near-zero false postives, then it probably makes sense > to be more assertive in how such VM-Exits are reported and logged. > Sorry, I should add RFC tag for this patch. I will add it next time.
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