From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) (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 A78293BB4A; Thu, 9 Apr 2026 20:36:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775766988; cv=none; b=cIIYNEW8iTyCyHoyn4rwIhZOh7eIUvizta++VM96SF9mJpXmmYOu+hqwOaOwTzrYZG6hDws1JsDJxKEDw4K53LMqf0yeq/Ccaws5VxBlZUHtYFGXL6bQ5zGZnbjyqNmokNHTodgYZO5RHjmG/Fb4awkX5EhHzMD08Zy3bWoiC8A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775766988; c=relaxed/simple; bh=gQuowERDs2CwnIxKTi48OK2lUNoHKjazh0NAg6vOHig=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jU6ZLwZH7+Fhl3uz5u9VINc42wC155fIvZHXgDu/W2lrkipcPZVZoMWHsiX4F0p34Mra0Y9o/lNRbeu5rQm6wXtMpiH8H1CWGAjiuaugcO1iBz839/99Q5YkVoLLTQjxgfqygS2g13iS9XpjsCazYCGhGU3jF8Fgyfn1KaEaKmI= 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=T3ZVRQeK; arc=none smtp.client-ip=198.175.65.14 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="T3ZVRQeK" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1775766987; x=1807302987; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=gQuowERDs2CwnIxKTi48OK2lUNoHKjazh0NAg6vOHig=; b=T3ZVRQeKbB33BVErx85W8FBNfDz3BdWRyzTz2YpND0yiDOHCfYqGtJp9 s/R0xya9G1CDcO0CC4QUeRHiSoF+oPNNckckEKjLdD5opu3QNupu2HGJD /CkxeYWBc5muAaF6Onntu9/MYndp4XyACc2aSn8DydLUmE54nToYHcDgL Onxt8ysfOEx+eTL0eiZ/DiU8RE92NxQGD0IUjNjML1q7vjzKteC0aKDVk nS2gGs+yc9VYA7/b3Gl7yXvwQBgYGJV43NoPRWV9BeXi2dW2h6gNkhHTD EorSqQ807mLl9QJdRFhzRoEoIPCBurvk2kjFhuwa/bWR7a8aCf7d+IHNi g==; X-CSE-ConnectionGUID: 0uxO33JbQVGV2XkMMEukGw== X-CSE-MsgGUID: F/tssg+lQY2FyNsJ21XGhA== X-IronPort-AV: E=McAfee;i="6800,10657,11754"; a="80643225" X-IronPort-AV: E=Sophos;i="6.23,170,1770624000"; d="scan'208";a="80643225" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Apr 2026 13:36:26 -0700 X-CSE-ConnectionGUID: gdIWAIm2Rj6zJdgyDMCvlQ== X-CSE-MsgGUID: p6gG8xayQ9u+FfGy3T8zPQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,170,1770624000"; d="scan'208";a="230608472" Received: from ray2.jf.intel.com (HELO [10.24.81.183]) ([10.24.81.183]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Apr 2026 13:36:24 -0700 Message-ID: <410df9f6-69ec-483f-9009-0a9b8c9162a9@intel.com> Date: Thu, 9 Apr 2026 13:36:02 -0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 02/10] x86/bhi: Make clear_bhb_loop() effective on newer CPUs To: Jim Mattson Cc: Pawan Gupta , x86@kernel.org, Jon Kohler , Nikolay Borisov , "H. Peter Anvin" , Josh Poimboeuf , David Kaplan , Sean Christopherson , Borislav Petkov , Dave Hansen , Peter Zijlstra , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , KP Singh , Jiri Olsa , "David S. Miller" , David Laight , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , David Ahern , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , Stanislav Fomichev , Hao Luo , Paolo Bonzini , Jonathan Corbet , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Asit Mallick , Tao Zhang , bpf@vger.kernel.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, chao.gao@intel.com References: <20260404002149.wtayv6a64vzuppgp@desk> <20260404034954.t7iapenzvhdpagxp@desk> <20260407163943.y6tkh26z2rfktn3y@desk> <20260407171151.2gf2idjbmph35ypb@desk> <20260407191128.b2hr2ttkdpyunhrr@desk> <20260407222738.lrartp6evfp7yhti@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/7/26 17:47, Jim Mattson wrote: > On Tue, Apr 7, 2026 at 4:41 PM Dave Hansen wrote: >> On 4/7/26 16:27, Jim Mattson wrote: >>> What is your proposed BHI_DIS_S override mechanism, then? >> Let me make sure I get this right. The desire is to: >> >> 1. Have hypervisors lie to guests about the CPU they are running on (for >> the benefit of large/diverse migration pools) >> 2. Have guests be allowed to boot with BHI_DIS_S for performance >> 3. Have apps in those guests that care about security to opt back in to >> BHI_DIS_S for themselves? > I just want guests on heterogeneous migration pools to properly > protect themselves from native BHI when running on host kernels at > least as far back as Linux v6.6. > > To that end, I would be satisfied with using the longer BHB clearing > sequence when HYPERVISOR is true and BHI_CTRL is false. If the guests can't get mitigation information from model/family because the hypervisor is lying (or may lie), then it's on the hypervisor to figure it out. I'm not sure we want to just assume that all hypervisors are going to lie all the time about this. I kinda think we should just let Pawan's series move forward and then we can debate the lying hypervisor problem once the series is settled.