Re: [PATCH v3 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

[Andy Lutomirski]

> On Mar 30, 2021, at 8:14 AM, Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> 
> On Mon, Mar 29, 2021, Andy Lutomirski wrote:
>> 
>>>> On Mar 29, 2021, at 7:04 PM, Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote:
>>> 
>>> 
>>>> 
>>>>> No, if these instructions take a #VE then they were executed at CPL=0.  MONITOR
>>>>> and MWAIT will #UD without VM-Exit->#VE.  Same for WBINVD, s/#UD/#GP.
>>>> 
>>>> Dare I ask about XSETBV?
>>> 
>>> XGETBV does not cause a #VE, it just works normally. The guest has full
>>> AVX capabilities.
>>> 
>> 
>> X *SET* BV
> 
> Heh, XSETBV also works normally, relative to the features enumerated in CPUID.
> XSAVES/XRSTORS support is fixed to '1' in the virtual CPU model.  A subset of
> the features managed by XSAVE can be hidden by the VMM, but attempting to enable
> unsupported features will #GP (either from hardware or injected by TDX Module),
> not #VE.

Normally in non-root mode means that every XSETBV results in a VM exit and, IIUC, there’s a buglet in that this happens even if CPL==3.  Does something special happen in TDX or does the exit get reflected back to the guest as a #VE?