From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2D150194082 for ; Fri, 8 Nov 2024 18:42:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731091347; cv=none; b=ueNrK1cczQabfHz/UIbvFef0uvdUrBLF4bbrlv4ZrpVOkjWv1sPyPJHr2UQ9/rC2x1wO4HjVs16YjnKe9nnlLgXTsbRCK6JhKcq8x4fjl5qdhxAJQ6ynv9aY7jllvHL6A9vVQ+mDHyIVX39JLZLzs3oHzk8x+ZuYIh59JrcEQAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731091347; c=relaxed/simple; bh=u2YGny6+IBZ3DloL7hyD6T4NLSl4ECJAfBNDdeOMha0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GQurl1UqT8j4rxXNvS4ke4Mpy4cigJEtz0UXdhQNylPMzq0doKEhOjpMSHO8uKJ6HeP5jJkxPKx/POjTjYkKbr60oVzoZiFFNduxYn86L64Xm4FwJ2nbTNClDZmeDZxzIenZ2g3WsJcrbN7gG7L/grFsa13HiGVhOY/xSXu1qmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=iwb6NAbN; arc=none smtp.client-ip=198.175.65.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="iwb6NAbN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1731091346; x=1762627346; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=u2YGny6+IBZ3DloL7hyD6T4NLSl4ECJAfBNDdeOMha0=; b=iwb6NAbNCe7zwjX5UUxGOHdrQTz1JwVc46S0JYx/f504N8RmMthi9W65 NQ/EuYpHeTiiGgd7dE5ioPaxVg6cPUFFf/tqFrqVa6gbh5f1JQrKhj/oq oNbPl22Gmp81LR948k/TTsLmhCb2indyPPUurAmYsb1Yy9DWKLIFUdeBO G7gPQjsCep9lA0+8KmeIAJCebW+G9r5o2PM1WAycPYY6Z4SwNFlXPF80h dvzeqezZNf640ETniTMdhaabeVfnDflYFwvy6ANy0M1ueWxAz7rDRrFSQ zvBfir3nXDI70Iheh6B1fUdlXwL1TzoL2ucLSMgCPAUq3j+XdErr1K52W w==; X-CSE-ConnectionGUID: 9IfIkPwYR6msfhrhjDelrQ== X-CSE-MsgGUID: 1sHg8HOnTfyj8nkGdFvH7A== X-IronPort-AV: E=McAfee;i="6700,10204,11250"; a="31089654" X-IronPort-AV: E=Sophos;i="6.12,138,1728975600"; d="scan'208";a="31089654" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Nov 2024 10:42:26 -0800 X-CSE-ConnectionGUID: aukTtv1gQ4yXx3VpQaSpfQ== X-CSE-MsgGUID: jYB4DQspTFqvRJETImTPlw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,138,1728975600"; d="scan'208";a="89652010" Received: from rfrazer-mobl3.amr.corp.intel.com (HELO [10.124.223.66]) ([10.124.223.66]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Nov 2024 10:42:25 -0800 Message-ID: <551e8238-84a1-4d5d-91c1-8d2adfde62e0@intel.com> Date: Fri, 8 Nov 2024 10:42:24 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/cpufeatures: Free up unused feature bits To: "H. Peter Anvin" , Sohil Mehta , x86@kernel.org, Borislav Petkov , Dave Hansen Cc: Thomas Gleixner , Ingo Molnar , Sean Christopherson , Tony Luck , linux-kernel@vger.kernel.org References: <20241107233000.2742619-1-sohil.mehta@intel.com> <7ff32a10-1950-434b-8820-bb7c3b408544@intel.com> <3492e85d-4aaa-4dd7-9e6a-c8fdc2aa2178@intel.com> <74338393-4F39-4A04-83B1-BA64CE2D2FDA@zytor.com> <4c01a30a-67d9-4918-8781-240b78944c42@intel.com> From: Dave Hansen Content-Language: en-US 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: <4c01a30a-67d9-4918-8781-240b78944c42@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/7/24 17:12, Dave Hansen wrote: > and then we recycled number 67: > > -#define X86_FEATURE_P3 ( 3*32+ 6) /* P3 */ > +#define X86_FEATURE_WHIZZY_NEW_FEATURE ( 3*32+ 6) /* P3 */ > > udev might try to load the old module on a new CPU with > X86_FEATURE_WHIZZY_NEW_FEATURE that's not a P3. Thinking about this a bit more... The kernel generates _both_ the "cpu:type:x86,ven*fam*mod*:feature:*0067*" string and the sysfs modalias string. So the issue isn't practically a mismatch between those. It's if some consumer of those fields (like /lib/udev/hwdb.d/) was looking for feature 67. The good news is that I don't see any of those today. But it's totally possible that folks have some crazy rules out there. So we should probably be _careful_ about changing those values and not just change them *ALL*. But I think it's pretty unlikely we'll break anybody by reusing a bit or two.