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SubjectRe: [PATCH RFC] KVM: x86: tell guests if the exposed SMT topology is trustworthy

> On 7 Nov 2019, at 16:02, Liran Alon <> wrote:
>> On 7 Nov 2019, at 16:00, Christophe de Dinechin <> wrote:
>> I share that concern about the naming, although I do see some
>> value in exposing the cpu_smt_possible() result. I think it’s easier
>> to state that something does not work than to state something does
>> work.
>> Also, with respect to mitigation, we may want to split the two cases
>> that Paolo outlined, i.e. have KVM_HINTS_REALTIME,
>> where CORES_CROSSTALKS indicates there may be some
>> cross-talk between what the guest thinks are isolated cores,
>> and CORES_LEAKING indicates that cores may leak data
>> to some other guest.
>> The problem with my approach is that it is shouting “don’t trust me”
>> a bit too loudly.
> I don’t see a value in exposing CORES_LEAKING to guest. As guest have nothing to do with it.

The guest could display / expose the information to guest sysadmins
and admin tools (e.g. through /proc).

While the kernel cannot mitigate, a higher-level product could for example
have a policy about which workloads can be deployed on a system which
may leak data to other VMs.


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