Re: [RFC v2-fix-v2 2/2] x86/tdx: Ignore WBINVD instruction for TDX guest

[Andi Kleen]

On 5/24/2021 4:42 PM, Dave Hansen wrote:
> On 5/24/21 4:32 PM, Kuppuswamy Sathyanarayanan wrote:
> > Functionally only DMA devices can notice a side effect from
> > WBINVD's cache flushing.
> This seems to be trying to make some kind of case that the only visible
> effects from WBINVD are for DMA devices.  That's flat out wrong.  It
> might be arguable that none of the other cases exist in a TDX guest, but
> it doesn't excuse making such a broad statement without qualification.

We're describing a few sentences down that guests run with EPT 
IgnorePAT=1, which is the qualification.

> Just grep in the kernel for a bunch of reasons this is wrong.
>
> Where did this come from?

Again the logic is very simple: TDX guest code is (mostly) about 
replacing KVM code with in kernel code, so we're just doing the same as 
KVM. You cannot get any more proven than that.


-Andi