From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.14]) (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 49C8B255E54; Fri, 2 May 2025 13:53:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746194013; cv=none; b=hMXuAAsJsCjMVqNtJXQzpHGEdKetp9VeUN+TZSYVAJ3Tt/SJ+cLeXRMvg2kM5A9gIGfVfPMV7XRI997o3acI6pbI0OdLBaYqscunk6YF0jx5ISoHR/YNMAE4JeAET5FdFaWEwU5pi8yeHR99nPAmEaOgUFXAOxziw5pB7r5K6mc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746194013; c=relaxed/simple; bh=LeoToeMCstsNjQeg4LXTjGxTobsjhD5xoUYnP0ZcFzk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XD6abhrHsnkXZ2JRsUylv/KIqnIOCwJAaMzRZcomlHpuVB+v/E5iZpduUKlEXdaWyxGyCG9bbMfWKTX5jdcTWE3ECMxNA+aTUw4/t0S7SWlku1ETM7vesyyFPVyWL+k8rLY8CRPqyiqOiTJ9OP2NIshpAQqmsYlrweaGWI7MNbU= 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=aIrex3JN; arc=none smtp.client-ip=192.198.163.14 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="aIrex3JN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1746194012; x=1777730012; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=LeoToeMCstsNjQeg4LXTjGxTobsjhD5xoUYnP0ZcFzk=; b=aIrex3JNTKasoU3Qe0T7cM+2LH/zarNJzt4CBPNDD4yNl7xDVghqifdK iZDQwq0jIvYc40jrFKDX3GkS0Q1JVOz/uE8rwwsOKqZ7LT4chUuqeXKIk icea2TE3b2yu19Ek5WfZJVzluyMSmNuifK19zIFhMzfLQcFRqMrkPC2+h DeiLzg7vE9zyV0uu+kCc7UzJLs77Ui1p//m7zaFpJ24kq0p8HrGzPKtnc +vS94RhgkvoiCjnyj/CQrmJc3WjO0oian9SDndLPsP2Y0fQIrQLfzNSan zRUEiOJ3yQKvbEponQrLCcKfwYeB3IBwl8i+cB6mKTwAXysHsWOmv8V1u A==; X-CSE-ConnectionGUID: 4HSc6NvbQFGQgMI7/XrqCg== X-CSE-MsgGUID: KUlDRxKQQIGkwsft5IUJMg== X-IronPort-AV: E=McAfee;i="6700,10204,11421"; a="48013471" X-IronPort-AV: E=Sophos;i="6.15,256,1739865600"; d="scan'208";a="48013471" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 May 2025 06:53:30 -0700 X-CSE-ConnectionGUID: Gm2K84tGReOY9bNQcutK0w== X-CSE-MsgGUID: 9PgngiGMRkyNHSp6md3TLA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.15,256,1739865600"; d="scan'208";a="134542729" Received: from ssimmeri-mobl2.amr.corp.intel.com (HELO [10.124.220.114]) ([10.124.220.114]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 May 2025 06:53:20 -0700 Message-ID: <34535b8c-35c8-4a7f-8363-f5a9c5a69023@intel.com> Date: Fri, 2 May 2025 06:53:17 -0700 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 00/25] context_tracking,x86: Defer some IPIs until a user->kernel transition To: Valentin Schneider , Steven Rostedt Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, linux-trace-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, Juri Lelli , Marcelo Tosatti , Yair Podemsky , Josh Poimboeuf , Daniel Wagner , Petr Tesarik , Nicolas Saenz Julienne , Frederic Weisbecker , "Paul E. McKenney" , Dave Hansen , Sean Christopherson , Juergen Gross , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Pawan Gupta , Paolo Bonzini , Arnd Bergmann , Jason Baron , Ard Biesheuvel , Luis Chamberlain , Petr Pavlu , Sami Tolvanen , Daniel Gomez , Naveen N Rao , Anil S Keshavamurthy , "David S. Miller" , Masami Hiramatsu , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Shuah Khan , Masahiro Yamada , Alice Ryhl , Miguel Ojeda , "Mike Rapoport (Microsoft)" , Rong Xu , Rafael Aquini , Song Liu , Andrii Nakryiko , Dan Carpenter , Brian Gerst , "Kirill A. Shutemov" , Benjamin Berg , Vishal Annapurve , Randy Dunlap , John Stultz , Tiezhu Yang References: <20250429113242.998312-1-vschneid@redhat.com> <20250430132047.01d48647@gandalf.local.home> <019f6713-cfbd-466b-8fb5-dcd982cf8644@intel.com> <20250430154228.1d6306b4@gandalf.local.home> 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: 7bit On 5/2/25 02:55, Valentin Schneider wrote: > My gripe with that was having two separate mechanisms > - super early entry around SWITCH_TO_KERNEL_CR3) > - later entry at context tracking What do you mean by "later entry"? All of the paths to enter the kernel from userspace have some SWITCH_TO_KERNEL_CR3 variant. If they didn't, the userspace that they entered from could have attacked the kernel with Meltdown. I'm theorizing that if this is _just_ about avoiding TLB flush IPIs that you can get away with a single mechanism.