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Re: [PATCH v3 1/3] amd/msr: implement VIRT_SPEC_CTRL for HVM guests on top of SPEC_CTRL
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 21 Apr 2022 11:34:47 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 21 Apr 2022 09:35:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 31.03.2022 11:27, Roger Pau Monne wrote:
> Use the logic to set shadow SPEC_CTRL values in order to implement
> support for VIRT_SPEC_CTRL (signaled by VIRT_SSBD CPUID flag) for HVM
> guests. 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.
>
> Some reasoning regarding why '!s' is used to annotate the feature:
> * '!': the feature might be exposed to guests even when not present
> on the host hardware.
As mentioned before I don't think ! is to be used for this particular
purpose. But this needs input from Andrew. Hence ...
> * 's': the feature won't be exposed by default.
>
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
... only tentatively:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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