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

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Date:   Tue, 30 Mar 2021 12:56:41 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD

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@...ux.intel.com>
> Reviewed-by: Andi Kleen <ak@...ux.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.

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

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