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Subject: Re: [PATCH v2 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD
To:     Dave Hansen <dave.hansen@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>
Cc:     Andi Kleen <ak@linux.intel.com>,
        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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 <0356a84a-765e-b20b-2efd-c5d94fc2347e@intel.com>
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Message-ID: <bab2b4b1-fa65-ecb9-e275-3e5ca4008d43@linux.intel.com>
Date:   Mon, 29 Mar 2021 15:42:55 -0700
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On 3/29/21 3:12 PM, Dave Hansen wrote:
> On 3/29/21 3:09 PM, Kuppuswamy, Sathyanarayanan wrote:
>>>>>> +    case EXIT_REASON_MWAIT_INSTRUCTION:
>>>>>> +        /* MWAIT is supressed, not supposed to reach here. */
>>>>>> +        WARN(1, "MWAIT unexpected #VE Exception\n");
>>>>>> +        return -EFAULT;
>>>>>
>>>>> How is MWAIT "supppressed"?
>>>> I am clearing the MWAIT feature flag in early init code. We should also
>>>> disable this feature in firmware.
>>>> setup_clear_cpu_cap(X86_FEATURE_MWAIT);
>>>
>>> I'd be more explicit about that.  Maybe even reference the code that
>>> clears the X86_FEATURE.
>> This change is part of the same patch.
> 
> Right, but if someone goes and looks at the switch() statement in 10
> years is it going to be obvious how MWAIT was "suppressed"?
Ok. I can add a comment line for it.
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer