Re: [PATCH v2] KVM: x86: Allow guests to see MSR_IA32_TSX_CTRL even if tsx=off

[Sean Christopherson]

On Mon, Feb 01, 2021, Paolo Bonzini wrote:
> On 01/02/21 09:46, Paolo Bonzini wrote:
> > > 
> > > This comment be updated to call out the new TSX_CTRL behavior.
> > > 
> > >     /*
> > >      * On TAA affected systems:
> > >      *      - nothing to do if TSX is disabled on the host.
> > >      *      - we emulate TSX_CTRL if present on the host.
> > >      *      This lets the guest use VERW to clear CPU buffers.
> > >      */
> > 
> > Ok.
> 
> Hmm, but the comment is even more accurate now than before, isn't it? It
> said nothing about hiding TSX_CTRL, so now it matches the code below.

Ha, that is technically true.  But it says "nothing to do..." and then clears a
flag.  The other interpretation of "nothing to do... at runtime" is also wrong
as KVM emulates the MSR as a nop.

I guess I just find the whole comment more confusing than the code itself.