From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.8]) (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 5BAC82EFD80; Mon, 20 Oct 2025 22:09:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.8 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760998185; cv=none; b=AgzsKGPV5RqgE6xEb1vJUKi5AfN66wDH+MUc9RL8ieLB7dPdzYqR0s9zdohnsORiapIokY4k6LYE2PnyZzy6EdKfqjQIk70P3u1ijYTZVKRnkAiRIf1whvaOzHmhUgnt3eDpYiKGWOifOFPazQrNHocgXv46DeQ4bpiwmja8nSg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760998185; c=relaxed/simple; bh=nlqSPPd+cTW53p798pcLtF/1icYvQ43dC5dy4j3mZcY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=l/Taa5OoSkvdciLktLIcaSnA2gb9eXiiFzu0pdQIUKni39aYpgm0zBpIfB+emfmxfCMvLO+N5XCFdEc45/bCeaVtwT+cUBXTAwlyq2fdSamP5Jh8FyrAgwpjPqcWdK3lz037dflE6S4tcCSXd23CaMvqTWjPDBBJdrPBXYfq4SE= 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=ShBPe1qQ; arc=none smtp.client-ip=192.198.163.8 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="ShBPe1qQ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1760998184; x=1792534184; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=nlqSPPd+cTW53p798pcLtF/1icYvQ43dC5dy4j3mZcY=; b=ShBPe1qQ9RPuKqjpEJsfnQWdrRguM67lorOpqnamqsHIjIfsPr/Mvc3A wQ0f8XMrpDa+gitV9UtRh+U6Z7SAKQYez5I3WXPaQCCw0YA2AwLuttyJB PHVCCgmBU8Uoenr5xiMTpJcZHhGZxSRYDJxjWT51Uxcx7gnhpuJFvCVcF /Ctm1OvxHjDPjjQGWZUUHxAO5M5wL0uJymIb71q2k/Atq7sOVWE2eiz3P o2NV293HoNdempidiXg9bIleS1VjXv+DG7H0iyHFaNMFPOS5nw8mC2Kl2 awUVifbWl/GfuKFqiuiX8VsIW6zH0UIHHw3i62KZPZS8tiwEAMToE3Usy g==; X-CSE-ConnectionGUID: hPs+yldVThKNZzUgm3JF6A== X-CSE-MsgGUID: ybI8khkYRMyQROWsuKmEPA== X-IronPort-AV: E=McAfee;i="6800,10657,11586"; a="80746789" X-IronPort-AV: E=Sophos;i="6.19,243,1754982000"; d="scan'208";a="80746789" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by fmvoesa102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Oct 2025 15:09:43 -0700 X-CSE-ConnectionGUID: y64OigoNR/O6hGjIJu0QGA== X-CSE-MsgGUID: KQXIJjrVSLCcIZBw5PB+qQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,243,1754982000"; d="scan'208";a="182625060" Received: from jdoman-mobl3.amr.corp.intel.com (HELO [10.125.108.101]) ([10.125.108.101]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Oct 2025 15:09:42 -0700 Message-ID: <225134fd-033f-4d63-b88c-772179054694@intel.com> Date: Mon, 20 Oct 2025 15:09:41 -0700 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/its: use Sapphire Rapids+ feature to opt out To: Pawan Gupta , Jon Kohler Cc: Thomas Gleixner , Borislav Petkov , Peter Zijlstra , Josh Poimboeuf , Jonathan Corbet , Ingo Molnar , Dave Hansen , "x86@kernel.org" , "H. Peter Anvin" , Brian Gerst , Brendan Jackman , "Ahmed S. Darwish" , Alexandre Chartre , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20251017011253.2937710-1-jon@nutanix.com> <20251020194446.w2s5f6nr7i7vw4ve@desk> <20251020204026.a7xuhnagsqo4otpx@desk> 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: <20251020204026.a7xuhnagsqo4otpx@desk> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/20/25 13:40, Pawan Gupta wrote: >> I can’t speak to other VMMs (e.g. vmw, hyperv, hyperscalers) and how they do >> it, but I suspect there are similar challenges around post-launch feature/bit >> additions that require the VM to be completely cold-booted. > Ok, that makes BUS_LOCK_DETECT a better choice than BHI_CTRL. I think it > be better to replace BHI_CTRL with BUS_LOCK_DETECT. Folks, I just think this kind of random feature spaghetti voodoo is a bad idea. Suppose X86_FEATURE_BUS_LOCK_DETECT is in silicon on an affected part but normally fused off. But a big customer shows up with a big checkbook and Intel releases microcode to enumerate X86_FEATURE_BUS_LOCK_DETECT on an affected part. What then? Your only choice is to convince Intel to make architectural the idea that X86_FEATURE_BUS_LOCK_DETECT is never enumerated on an affected part. Because even if we go forward with that patch we've *DONE* that in Linux: we've made it de facto architecture and Intel can never change it. Can someone try to boil down the problem statement for me again, please? VMs are slow because of mitigations for issues to which they are not vulnerable when running old kernels on old hypervisors. Is that it?