Re: [PATCH v8 2/6] KVM: x86: Virtualize CR4.LAM_SUP

[Huang, Kai]

> > >   
> > LAM only applies to 64-bit linear address, which means LAM can only be enabled
> > when CPU is in 64-bit mode with either 4-level or 5-level paging enabled.
> > 
> > What's the hardware behaviour if we set CR4.LAM_SUP when CPU isn't in 64-bit
> > mode?  And how does VMENTRY check GUEST_CR4.LAM_SUP and 64-bit mode?
> > 
> > Looks they are not clear in the spec you pasted in the cover letter:
> > 
> > https://cdrdv2.intel.com/v1/dl/getContent/671368
> > 
> > Or I am missing something?
> Yes, it is not clearly described in LAM spec.
> Had some internal discussions and also did some tests in host,
> if the processor supports LAM, CR4.LAM_SUP is allowed to be set even 
> when cpu isn't in 64bit mode.
> 
> There was a statement in commit message of the last version, but I 
> missed it in this version. I'll add it back.
> "CR4.LAM_SUP is allowed to be set even not in 64-bit mode, but it will not
> take effect since LAM only applies to 64-bit linear address."

Yeah this does help.  Please add it back to the changelog.

> 
> Also, I will try to ask Intel guys if it's possible to update the document.
> 

Thanks.