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Subject: Re: [PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD
To:     Dave Hansen <dave.hansen@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Xiaoyao Li <xiaoyao.li@intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        linux-kernel@vger.kernel.org
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 <840efd72-65b1-385c-e9a6-343410c85221@intel.com>
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Message-ID: <770415c9-38d7-08fc-e255-56c168967b7c@linux.intel.com>
Date:   Tue, 30 Mar 2021 10:02:53 -0700
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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