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

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Date:   Tue, 30 Mar 2021 10:02:53 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        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 3/30/21 8:10 AM, Dave Hansen wrote:
> On 3/30/21 8:00 AM, Andi Kleen wrote:
>>>> +	/* 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.
> 
> If this MWAIT behavior (clearing the CPUID bit) is part of the guest
> architecture, then it would also be appropriate to WARN() rather than
> silently clearing the X86_FEATURE bit.
Makes sense. It will be useful to find the problem with TDX Module.
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer