Re: [Xen-devel] MSR_SPEC_CTRL intercept

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.05.18 at 00:09, <andrew.cooper3@xxxxxxxxxx> wrote:
> It is, as documented, not completely strictly true (according to the
> latest revision of the spec), but is there deliberately to simply so we
> don't give the guest implausible configurations.  There is not a
> processor with STIBP but without IBRSB, nor is there one with SSBD
> without STIBP or IBRSB, and it is unlikely that future processors would
> change this arrangement.

As pointed out elsewhere I believe this is a wrong dependency to make,
even if perhaps current or past Intel docs suggest so (AMD ones don't
for their versions of the features). Wile it may be the case that there's
currently no case in practice with SSBD but no IBRSB, I don't see why
this would need to remain that way. The two things are strictly
independent.

I very much think there should be an indicator of the MSR itself
existing, set to the OR of any of the bits in the MSR that are valid.
Shouldn't such a mask anyway be part of struct msr_domain_policy
(as a companion to the current value of the MSR per vCPU)?

Jan



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