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This includes using the spec_ctrl vCPU MSR variable to store > the guest set value of VIRT_SPEC_CTRL.SSBD, which will be OR'ed with > any SPEC_CTRL values being set by the guest. > > On hardware having SPEC_CTRL VIRT_SPEC_CTRL will not be offered by > default to guests. VIRT_SPEC_CTRL will only be part of the max CPUID > policy so it can be enabled for compatibility purposes. > > Note that '!' is used in order to tag the VIRT_SSBD feature as > specially handled. It's possible for the feature to be available to > guests on hardware that doesn't support it natively, for example when > implemented as done by this patch on top of SPEC_CTRL.SSBD (AMD_SSBD). Except for this ! aspect the change looks good to me, but in order to give my R-b this aspect needs sorting. Andrew - what are your thoughts here? The reason cited by Roger doesn't look to be one that I so far understood would require use of !, but your intentions may well have been different from what my current understanding is. Jan