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a="191886981" X-IronPort-AV: E=Sophos;i="5.81,291,1610438400"; d="scan'208";a="191886981" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2021 08:10:27 -0700 IronPort-SDR: oi7Yyfuch8HZERJecHeQqRr5F2Mu2hMYnxOFYheUaNBe5/MmXFsoF6unp/DilhQe9Q44PBq+og QtEObkzjXBnQ== X-IronPort-AV: E=Sophos;i="5.81,291,1610438400"; d="scan'208";a="411669270" Received: from tkokeray-mobl.amr.corp.intel.com (HELO [10.252.143.165]) ([10.252.143.165]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2021 08:10:26 -0700 Subject: Re: [PATCH v1 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD To: Andi Kleen , Xiaoyao Li Cc: Kuppuswamy Sathyanarayanan , Peter Zijlstra , Andy Lutomirski , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Dan Williams , Raj Ashok , Sean Christopherson , linux-kernel@vger.kernel.org References: <331b34e3d6153f0a7b0ab0a9a8cb5de71f0bfd93.1616803999.git.sathyanarayanan.kuppuswamy@linux.intel.com> <20210330150048.GB1285835@tassilo.jf.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210330150048.GB1285835@tassilo.jf.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.