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X-IronPort-AV: E=McAfee;i="6600,9927,10740"; a="348139699" X-IronPort-AV: E=Sophos;i="6.00,241,1681196400"; d="scan'208";a="348139699" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Jun 2023 17:24:56 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10740"; a="781895307" X-IronPort-AV: E=Sophos;i="6.00,241,1681196400"; d="scan'208";a="781895307" Received: from clin147-mobl.amr.corp.intel.com (HELO [10.212.134.227]) ([10.212.134.227]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Jun 2023 17:24:55 -0700 Message-ID: <6e3ae1bd-c6e4-b7cb-ab4c-50849ffbc237@intel.com> Date: Tue, 13 Jun 2023 17:24:54 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v11 18/20] x86: Handle TDX erratum to reset TDX private memory during kexec() and reboot Content-Language: en-US To: "Huang, Kai" , "kirill.shutemov@linux.intel.com" Cc: "kvm@vger.kernel.org" , "Luck, Tony" , "david@redhat.com" , "bagasdotme@gmail.com" , "ak@linux.intel.com" , "Wysocki, Rafael J" , "linux-kernel@vger.kernel.org" , "Chatre, Reinette" , "Christopherson,, Sean" , "pbonzini@redhat.com" , "tglx@linutronix.de" , "linux-mm@kvack.org" , "Yamahata, Isaku" , "Shahar, Sagi" , "peterz@infradead.org" , "imammedo@redhat.com" , "Gao, Chao" , "Brown, Len" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "Huang, Ying" , "Williams, Dan J" References: <5aa7506d4fedbf625e3fe8ceeb88af3be1ce97ea.1685887183.git.kai.huang@intel.com> <20230609132301.uvvp27yr5kpenl6f@box.shutemov.name> <58f34b4b81b6d6b37d3386dec0f073e6eb7a97ff.camel@intel.com> <20230612075830.jbrdd6ysz4qq7wdf@box.shutemov.name> <4c7effc3abe71aa1cbee41f3bd46b97aed40be26.camel@intel.com> <48d5a29a-878c-665d-6ac2-6f0563bf6f3c@intel.com> <3bbb6b384ba89dfaa13be01654ad27e41d779fba.camel@intel.com> <6fb1ec2f-8713-8191-fd31-751b1a663b0b@intel.com> <1542a26c0501cb9f7fc330d8aa27e565c81b969c.camel@intel.com> From: Dave Hansen In-Reply-To: <1542a26c0501cb9f7fc330d8aa27e565c81b969c.camel@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: m9jhweznhyomcdtrotnfp7bettnox8eb X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 458344000B X-Rspam-User: X-HE-Tag: 1686702298-15525 X-HE-Meta: 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 EhexNyjt g1pCD43g67xFpf3b67DptlFa60yNHcgyU2GZMLO3Kca9J0fySw5kweIyT047Pfhh10XFAUYXam96nPeNRTk+bn3kWUeVAiUJluYFAspbPmDbcOpgh8C0nJIE4FFzbz3vjqNjip2o1ZbGLFIEclRzKyVhNflLgklis7ZdmkT7pAn8eYiFb8WDOSwPnjHGf4sUPYqtx X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/13/23 16:18, Huang, Kai wrote: > On Tue, 2023-06-13 at 07:25 -0700, Hansen, Dave wrote: >> On 6/12/23 17:51, Huang, Kai wrote: >>> If we introduce a helper to mark a page as TDX private page, >> Let me get this right: you have working, functional code for a >> highly-unlikely scenario (kernel bugs or even more rare hardware >> errors). But, you want to optimize this super-rare case? It's not fast >> enough? >> >> Is there any other motivation here that I'm missing? >> > No it's not about speed. The motivation is to have a common code to yield less > line of code, though I don't have clear number of how many LoC can be reduced. OK, so ... ballpark. How many lines of code are we going to _save_ for this super-rare case? 10? 100? 1000? The upside is saving X lines of code ... somewhere. The downside is adding Y lines of code ... somewhere else and maybe breaking things in the process. You've evidently done _some_ kind of calculus in your head to make this tradeoff worthwhile. I'd love to hear what your calculus is, even if it's just a gut feel. Could you share your logic here, please?