Re: [Xen-devel] [PATCH 8/9] x86/amd: Virtualise MSR_VIRT_SPEC_CTRL for guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.12.18 at 20:09, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 05/12/2018 08:41, Jan Beulich wrote:
>>>>> On 04.12.18 at 22:35, <Brian.Woods@xxxxxxx> wrote:
>>> The other thing I don't get is why advertise virtualized SSBD when the
>>> guest setting it does nothing?  If ssbd_opt=true is set, as the code is
>>> now, why even advertise it to the guest?  I'd suggest either allowing
>>> the guest to turn it off or not advertise it at all (when ssbd_opt =
>>> true).
>> I think it's better to advertise the feature nevertheless: Otherwise
>> the guest might either try some other way of mitigating the
>> (believed) vulnerability, or it may report in its logs that it's vulnerable
>> (without mitigation) when it really isn't.
> 
> opt_ssbd=true is there for the truly paranoid, and noone uses it in
> practice.

Be careful with such claims. From logs I've seen I know different. (I'm
not going to claim though that I'm sure they really know why they do
so, but you need to accept reasons like "just to be on the safe side".)

Jan



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