Re: [Xen-devel] [PATCH 0/9] xen/amd: Support for guest MSR_VIRT_SPEC_CTRL support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.12.18 at 17:18, <andrew.cooper3@xxxxxxxxxx> wrote:
> This is a lingering TODO item from XSA-263.  It adds support AMD's
> MSR_VIRT_SPEC_CTRL interface, and changes Xen's "boot time global" SSBD
> setting into a per-vcpu setting.
> 
> This can be found on:
>   git://xenbits.xen.org/people/andrewcoop/xen.git xen-virt-spec-ctrl-v1
> 
> The start of the series is some cleanup.  It then teaches Xen to recognise the
> available interfaces (including MSR_VIRT_SPEC_CTRL from a hypervisor), then
> how to safely context switch the per-core LS_CFG on Fam17h, an finally to
> expose support to guests.
> 
> I've got some further MSR work coming because we have to fix the
> default-leakiness of MSRs in this range, because a guest becomes unsafe to
> migrate as soon as it reads any of the pipeline control MSRs.

I've seen you mention this elsewhere, but I'm still unclear about
the "why" part here.

Jan



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