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 7CA09C54798 for ; Thu, 7 Mar 2024 21:48:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DAE176B02C8; Thu, 7 Mar 2024 16:48:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D5D686B02CB; Thu, 7 Mar 2024 16:48:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BFDAC6B02CC; Thu, 7 Mar 2024 16:48:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id B05966B02C8 for ; Thu, 7 Mar 2024 16:48:33 -0500 (EST) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 63681C11D3 for ; Thu, 7 Mar 2024 21:48:33 +0000 (UTC) X-FDA: 81871582506.05.6967747 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.12]) by imf29.hostedemail.com (Postfix) with ESMTP id 2529E12000D for ; Thu, 7 Mar 2024 21:48:29 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=fE8La19P; spf=pass (imf29.hostedemail.com: domain of dave.hansen@intel.com designates 192.198.163.12 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1709848111; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=kSc+0NWNenKNnnjKmdcMqJ+k1feaiVQn6i33PqyK5xQ=; b=mOwUc849MXTAB0iXzOumOoNkiBMNkJPgdN3yi772ke5tL8ujlRckWYdLUUxbkROfgoIAaq UeXymPwiZJbbTlkLUM+fQChP2cLPSSTyO0FIJ99zkNvwn5QzFPcEm1cXCfot/GpatC1vWL omYXMdGrlKtBTYEGCuqvcus38inDIog= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=fE8La19P; spf=pass (imf29.hostedemail.com: domain of dave.hansen@intel.com designates 192.198.163.12 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1709848111; a=rsa-sha256; cv=none; b=uj15TtolQmArsfl+itjlxSIifO3QibuPvupKjWXpFMKHwoO83MKKQc1f4uPljbg2HQj2rH fCEN6KrxywGm/gUU3RByYrdnV1n3M23gL5VTnu1t+Riqoe2793YZ6ZBnQKICh6A0pcs2dQ mcsqzoGdX/gQzU3Vhe5GAXTXNm5R59Y= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1709848111; x=1741384111; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=IT2dpYQ6uHucwWrvvg6K56c2aMW3hbQgLU4g02htMiM=; b=fE8La19P6SKL2EiPo7LeeecT86V9BURVbcuqwaT/W7ft1skBItH8eGSS J+ywZq5i0IvNPb4DZwyEo6lmViNHceCvXdLWw7wqVjpc9k9VYm8dpjWDI IVe8A3LkOwpEmk3oZgVJHWQchtAjplrCiGY81Ge0qmdQD6xvWL59fb4MH 26wJyxWbD9s/z3qPX7pTSb7R1OlwKcT4YeE7c/BZc2/iURuAxW4khWAwf 0WD4vGJuGKVG4zNvbYOm6NPZDNF1yQb3Efqb1RrSKRyommYR3ZtzEceF6 7CIT9PaNqpCALimY3wzLnUqYT3b0c1CoFw9/U+dVOqwwNN34ohxvK29aa A==; X-IronPort-AV: E=McAfee;i="6600,9927,11006"; a="8306853" X-IronPort-AV: E=Sophos;i="6.07,107,1708416000"; d="scan'208";a="8306853" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Mar 2024 13:48:30 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,107,1708416000"; d="scan'208";a="33398194" Received: from yuqiangu-mobl.amr.corp.intel.com (HELO [10.209.57.176]) ([10.209.57.176]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Mar 2024 13:48:29 -0800 Message-ID: Date: Thu, 7 Mar 2024 13:48:28 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/3] x86/mm: make sure LAM is up-to-date during context switching Content-Language: en-US To: Yosry Ahmed Cc: "Kirill A. Shutemov" , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Andy Lutomirski , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240307133916.3782068-1-yosryahmed@google.com> <20240307133916.3782068-3-yosryahmed@google.com> <034466a4-0917-47c4-934b-9549c3076624@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 2529E12000D X-Rspam-User: X-Stat-Signature: 45sdhrbg776wjaxyjpzjxtajsdpsxecs X-Rspamd-Server: rspam01 X-HE-Tag: 1709848109-660318 X-HE-Meta: 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 xaJGXs5b WKZBYXuBxpjhRl55njdsdwBnc9dpgqJDQynZ/2QcEbIA8JZAA7woSpW7KkogzkgqEM/gmmbBEmZ16jDyJcj5wLZlZyi4rOAyNkualzSjqyp80bYnRTum2z3r1tDTlzOr/MwKnzRMX8jW6e7+g3P9NIL6h1FTUU/tYZiTF2U3BJ4dL4pzUPzQnEoCSHw== 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: List-Subscribe: List-Unsubscribe: On 3/7/24 13:08, Yosry Ahmed wrote: > CPU 1 CPU 2 > /* user thread running */ > context_switch() /* to kthread */ > /* user thread enables LAM */ > context_switch() > context_switch() /* to user thread */ > > In this case, there are no races, but the second context switch on CPU 1 > may not write CR3 (if TLB is up-to-date), in which case we will run the > user thread with CR3 having the wrong LAM mask. This could cause bigger > problems, right? Yes, but this is precisely the kind of thing that we should solve with mm generations. Its sole purpose is to thwart optimization where the mm_prev==mm_next and might not rewrite CR3.