Re: [PATCH v6 0/3] amd/msr: implement MSR_VIRT_SPEC_CTRL for HVM guests

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.05.2022 17:31, Roger Pau Monne wrote:
> Hello,
> 
> The following series implements support for MSR_VIRT_SPEC_CTRL
> (VIRT_SSBD) on different AMD CPU families.
> 
> Note that the support is added backwards, starting with the newer CPUs
> that support MSR_SPEC_CTRL and moving to the older ones either using
> MSR_VIRT_SPEC_CTRL or the SSBD bit in LS_CFG.
> 
> Xen is still free to use it's own SSBD setting, as the selection is
> context switched on vm{entry,exit}.
> 
> On Zen2 and later, SPEC_CTRL.SSBD should exist and should be used in
> preference to VIRT_SPEC_CTRL.SSBD.  However, for migration
> compatibility, Xen offers VIRT_SSBD to guests (in the max cpuid policy,
> not default) implemented in terms of SPEC_CTRL.SSBD.
> 
> On Fam15h thru Zen1, Xen exposes VIRT_SSBD to guests by default to
> abstract away the model and/or hypervisor specific differences in
> MSR_LS_CFG/MSR_VIRT_SPEC_CTRL.
> 
> So the implementation of VIRT_SSBD exposed to HVM guests will use one of
> the following underlying mechanisms, in the preference order listed
> below:
> 
>  * SPEC_CTRL.SSBD: patch 1
>  * VIRT_SPEC_CTRL.SSBD: patch 2.
>  * Non-architectural way using LS_CFG: patch 3.
> 
> NB: patch 3 introduces some logic in GIF=0 context, such logic has been
> kept to a minimum due to the special context it's running on.
> 
> Roger Pau Monne (3):
>   amd/msr: implement VIRT_SPEC_CTRL for HVM guests on top of SPEC_CTRL
>   amd/msr: allow passthrough of VIRT_SPEC_CTRL for HVM guests
>   amd/msr: implement VIRT_SPEC_CTRL for HVM guests using legacy SSBD

FTAOD, while besides a missing ack for ...

>  CHANGELOG.md                                |   3 +

... this addition the series would now look to be ready to go in,
I'd like to have some form of confirmation by you, Andrew, that
you now view this as meeting the comments you gave on an earlier
version.

Jan