From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C3CCEB64D7 for ; Tue, 20 Jun 2023 07:58:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AF7E38D0003; Tue, 20 Jun 2023 03:58:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AA8EC8D0001; Tue, 20 Jun 2023 03:58:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 970398D0003; Tue, 20 Jun 2023 03:58:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 8599C8D0001 for ; Tue, 20 Jun 2023 03:58:39 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 63E461C8456 for ; Tue, 20 Jun 2023 07:58:39 +0000 (UTC) X-FDA: 80922374358.16.40E2A44 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf27.hostedemail.com (Postfix) with ESMTP id 495FB40013 for ; Tue, 20 Jun 2023 07:58:37 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=de+bOqx9; spf=none (imf27.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1687247917; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=BZECT2dbtdQzJxRKjUga30Xmntvvyra9f2PegQf5YA4=; b=BUBhv4OKasEKMiuZNzOqmWuj/CI97G07Dd3nF5bTbFGcnnXffKeM8JjwnVQW2JGIJxEsrT 32EMTRAH8QzeqEgNlhoqMTo36NzKriZrkxTPyym5hQ6QnFkz8YKzZS1QgkXXntKz0FygQ6 dHqmbWZvYhCqbn2hXX5mbK3aWbJGOEY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1687247917; a=rsa-sha256; cv=none; b=aVyNKcWC9YtW3vzUyQJPJ/vQIi2xFVwEsUGReuwHHUDBybK6mGQfKJmRLVboLYbMGW+VHP EyfyOKoD4FpoEccLYQEWAAGR9znUBahE1mwT2f71R0hULNJat/3L1TL49E4UhR4FdofSfg fGfhNZDY6IsV9OYuR5AX3hZh7GSrNI4= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=de+bOqx9; spf=none (imf27.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=none DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=BZECT2dbtdQzJxRKjUga30Xmntvvyra9f2PegQf5YA4=; b=de+bOqx9/anW6oVh6YmJvCVeRR cYjE9B4blJW5E8eOr/pwAy/iz6GLAI9SJ6i2rNJlNTKQIiM9cHnB0K8OA0mU4bFO1Jk06PWASYn8P SkD1gZN4oKesbZpa4qAReA45F4ruvysyYc9AdwskypURpGcSd/9mjE9VezWYFlnH9wNP6qPP5MH+4 p1LyFzVLLaFyz1lLBcsehIq/aGPiNV556lTvkjb6N8cMgYGwgvFzGhle4157+xORsSlDilkCIfN5S UIvKqIK2Iw9qf/PzBNxrrFZWN+oqj2Yl1bF27J6i9XKaCR75QgH/LkXyl2Rme8RXEHwSdfHCtLia0 0cBxtrSw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qBWG0-00Cphv-05; Tue, 20 Jun 2023 07:58:32 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 2C12B30020B; Tue, 20 Jun 2023 09:58:31 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 0802123BE1E49; Tue, 20 Jun 2023 09:58:30 +0200 (CEST) Date: Tue, 20 Jun 2023 09:58:30 +0200 From: Peter Zijlstra To: Dave Hansen Cc: "Huang, Kai" , "kirill.shutemov@linux.intel.com" , "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" , "imammedo@redhat.com" , "Gao, Chao" , "Brown, Len" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "Huang, Ying" , "Williams, Dan J" Subject: Re: [PATCH v11 18/20] x86: Handle TDX erratum to reset TDX private memory during kexec() and reboot Message-ID: <20230620075830.GU4253@hirez.programming.kicks-ass.net> References: <58f34b4b81b6d6b37d3386dec0f073e6eb7a97ff.camel@intel.com> <20230612075830.jbrdd6ysz4qq7wdf@box.shutemov.name> <4c7effc3abe71aa1cbee41f3bd46b97aed40be26.camel@intel.com> <48d5a29a-878c-665d-6ac2-6f0563bf6f3c@intel.com> <5782c8c2bb3e76a802e4a81c553a21edbaee7c47.camel@intel.com> <20230619144651.kvmscndienyfr3my@box.shutemov.name> <63477d22-26ef-dd08-a3b0-93931b7d1d16@intel.com> <0be5634f390015ee6badb3f2b2154ad90eb70434.camel@intel.com> <4069285d-1653-4cbf-a3b3-24727697754b@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4069285d-1653-4cbf-a3b3-24727697754b@intel.com> X-Rspamd-Queue-Id: 495FB40013 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 9tn6gqhkj1junddqg3ay3qhw9qx8ymym X-HE-Tag: 1687247917-613816 X-HE-Meta: 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 lPpESkCc 996LtYzZp5HyikaVL7gsWoUv2rykHZ/vE1c8hBPrO2jmNO0ItjDbVZI0Bt2/QCKdETlGAoU2NZ9Sa0/ORRSml7CLZM4FBpJXtbKeC/qLib7CEPinMIokdnrr/DJlJ5MukRFR90Kn690WbgRz2ulK7y1TJ7jh42Z0JbQxbs8iRgQTRJXMEowDPwKQCeQ== 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 Mon, Jun 19, 2023 at 06:06:30PM -0700, Dave Hansen wrote: > On 6/19/23 17:56, Huang, Kai wrote: > > Any comments to below? > > Nothing that I haven't already said in this thread: > > > Just use a normal old atomic_t or set_bit()/test_bit(). They have > > built-in memory barriers are are less likely to get botched. > > I kinda made a point of literally suggesting "atomic_t or > set_bit()/test_bit()". I even told you why: "built-in memory barriers". > > Guess what READ/WRITE_ONCE() *don't* have. Memory barriers. x86 has built-in memory barriers for being TSO :-) Specifically all barriers provided by spinlock (acquire/release) are no-ops on x86. (strictly speaking locks imply stronger order than they have to because TSO atomic ops imply stronger ordering than required) There is one (and only the one) re-ordering possible on TSO and that is the store-buffer, later loads can fail to observe prior stores. If that is a concern, you need explicit barriers. This is #MC, much care and explicit open-coded crap is expected. Also, this is #MC, much broken is also expected :-( As in, the current #MC handler is a know pile of shit. Basically the whole of #MC should be noinstr -- it isn't and that's a significant problem. Also we still very much suffer the NMI <- #MC problem and the #MC latch is known broken garbage. Whatever you do, do it very carefully, double check and be more careful.