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X-IronPort-AV: E=McAfee;i="6600,9927,10762"; a="427040560" X-IronPort-AV: E=Sophos;i="6.01,183,1684825200"; d="scan'208";a="427040560" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2023 07:34:08 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10762"; a="713217660" X-IronPort-AV: E=Sophos;i="6.01,183,1684825200"; d="scan'208";a="713217660" Received: from subrator-mobl1.amr.corp.intel.com (HELO [10.209.29.125]) ([10.209.29.125]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2023 07:34:06 -0700 Message-ID: <1a8099e2-da28-6b2a-7b5a-1d6346b7f95d@intel.com> Date: Wed, 5 Jul 2023 07:34:06 -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 v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on demand Content-Language: en-US To: Peter Zijlstra , Sean Christopherson Cc: Isaku Yamahata , Kai Huang , "kvm@vger.kernel.org" , Ashok Raj , Tony Luck , "david@redhat.com" , "bagasdotme@gmail.com" , "ak@linux.intel.com" , Rafael J Wysocki , "kirill.shutemov@linux.intel.com" , Reinette Chatre , "pbonzini@redhat.com" , "mingo@redhat.com" , "tglx@linutronix.de" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Isaku Yamahata , "nik.borisov@suse.com" , "hpa@zytor.com" , Sagi Shahar , "imammedo@redhat.com" , "bp@alien8.de" , Chao Gao , Len Brown , "sathyanarayanan.kuppuswamy@linux.intel.com" , Ying Huang , Dan J Williams , "x86@kernel.org" References: <104d324cd68b12e14722ee5d85a660cccccd8892.1687784645.git.kai.huang@intel.com> <20230628131717.GE2438817@hirez.programming.kicks-ass.net> <0c9639db604a0670eeae5343d456e43d06b35d39.camel@intel.com> <20230630092615.GD2533791@hirez.programming.kicks-ass.net> <2659d6eef84f008635ba300f4712501ac88cef2c.camel@intel.com> <20230630183020.GA4253@hirez.programming.kicks-ass.net> <20230630190514.GH3436214@ls.amr.corp.intel.com> <20230704165836.GB462772@hirez.programming.kicks-ass.net> From: Dave Hansen In-Reply-To: <20230704165836.GB462772@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 71036100026 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 4rjqem7rcyspge3cf6akyh3hno1euqom X-HE-Tag: 1688567723-65972 X-HE-Meta: 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 FXJAy0yV FUv96Y5zrF7HrxOjnOWn9VL9NJR1LnHG8wQi3oq0OoAr5czATAzMrBfmHwkL8nHpU/H5kgT5XYtqrAJnY5UsEc4/zqB5XGs0Eh3702YPYiV4VBZy1XnEC/2nvEQSVLRvTWcWNV5XgCvSsrlYqkFH3UyNDvOVxwnN4n21H/xu6fSwQfrzzXj3snW/fwTRcBKSVyyXj2D+CH8A5l6KnrrH9isy/CnR5j+MFEx55hrbczy63Xl2Yfm9Jz23jfKc4Z2+sJRbe X-Bogosity: Ham, tests=bogofilter, spamicity=0.000275, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 7/4/23 09:58, Peter Zijlstra wrote: > If we have concerns about allocating the PAMT array, can't we use CMA > for this? Allocate the whole thing at boot as CMA such that when not > used for TDX it can be used for regular things like userspace and > filecache pages? I never thought of CMA as being super reliable. Maybe it's improved over the years. KVM also has a rather nasty habit of pinning pages, like for device passthrough. I suspect that means that we'll have one of two scenarios: 1. CMA works great, but the TDX/CMA area is unusable for KVM because it's pinning all its pages and they just get moved out of the CMA area immediately. The CMA area is effectively wasted. 2. CMA sucks, and users get sporadic TDX failures when they wait a long time to run a TDX guest after boot. Users just work around the CMA support by starting up TDX guests at boot or demanding a module parameter be set. Hacking in CMA support was a waste. Am I just too much of a pessimist?