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

[Xiaoyao Li]

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@xxxxxxxxxxxxxxx>
> Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> ---
>
> 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.

Do we still need to safeguard it by setup_clear_cpu_cap() here?

> +
>   	tdg_get_info();
>   
>   	pv_ops.irq.safe_halt = tdg_safe_halt;