Re: [PATCH v2] x86: Skip WBINVD instruction for VM guest

Dan Williams
2021-12-06T17:51:19Z

On Mon, Dec 6, 2021 at 8:54 AM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 12/6/21 8:39 AM, Dan Williams wrote:
> >> But, the trick is that we need a contract. A contract requires a
> >> "meeting of the minds" first.
> > The WBINVD requirement in sleep states is about getting cache contents
> > out to to power preserved domain before the CPU turns off. The bare
> > metal host handles that requirement. The conversation that needs to be
> > had is with the ACPI specification committee to clarify that virtual
> > machines have no responsibility to flush caches. We can do that as a
> > Code First proposal to the ACPI Specification Working Group.
>
> Sounds sane to me. So, we effectively go to the ACPI folks and say that
> Linux isn't going to do WBINVD in virtualized environments any more.
> That was effectively the approach that the first patch in this thread did:
>
> > https://lore.kernel.org/all/20211116005027.2929297-1-sathyanarayanan.kuppuswamy@linux.intel.com/
>
> Right?

Correct, my reviewed-by was based on that observation, and now we can
close the loop by proposing the specification change.