Re: [PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

[Andi Kleen <ak@linux.intel.com>]

On Tue, Mar 30, 2021 at 12:56:41PM +0800, Xiaoyao Li wrote:
> On 3/27/2021 8:18 AM, Kuppuswamy Sathyanarayanan wrote:
> > In non-root TDX guest mode, MWAIT, MONITOR and WBINVD instructions
> > are not supported. So handle #VE due to these instructions as no ops.
> > 
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > Reviewed-by: Andi Kleen <ak@linux.intel.com>
> > ---
> > 
> > Changes since previous series:
> >   * Suppressed MWAIT feature as per Andi's comment.
> >   * Added warning debug log for MWAIT #VE exception.
> > 
> >   arch/x86/kernel/tdx.c | 23 +++++++++++++++++++++++
> >   1 file changed, 23 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> > index e936b2f88bf6..fb7d22b846fc 100644
> > --- a/arch/x86/kernel/tdx.c
> > +++ b/arch/x86/kernel/tdx.c
> > @@ -308,6 +308,9 @@ void __init tdx_early_init(void)
> >   	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> > +	/* MWAIT is not supported in TDX platform, so suppress it */
> > +	setup_clear_cpu_cap(X86_FEATURE_MWAIT);
> 
> In fact, MWAIT bit returned by CPUID instruction is zero for TD guest. This
> is enforced by SEAM module.

Good point.
> 
> Do we still need to safeguard it by setup_clear_cpu_cap() here?

I guess it doesn't hurt to do it explicitly.


-Andi