From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.20]) (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 A4F56DF58; Fri, 24 Jan 2025 16:23:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.20 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737735802; cv=none; b=j43iM2P7EaEP3yIXW+nW+6ldkgwMXYXIJHU9LPsKFl3ZQ4GSSAFJfTIxsywXL8YZsjkdvQbR97JM1tmQ9OfkGbOlJyOsyTHMkWm/PYzveZ9+FQktdZ2WKQzTs3iM5kcpTDtcNsNFCouN26TzTCS7Djus5nBQHkaI/7KqiMnRJVU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737735802; c=relaxed/simple; bh=q8NwVv09wJhDznWuX35FkcGuw83e+u+Ce9LHxusy1eA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Qx+pXQRVztRrr44/kOvXoHmXM6Bz0haiC6waFhO69Sz+tZ4tquE7f8LsAXk1mmqyEnZpsb+HVkgXEeXVGyeaDTOLZolldmxb8da43ZDcuDuKFrWg2AeebQlgJpJRwzm3CBGrIofJBZ4Zm/Zik5ygA+yyq5o0QagxWmJHPVEuvQE= 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=U37pl3er; arc=none smtp.client-ip=198.175.65.20 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="U37pl3er" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1737735802; x=1769271802; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=q8NwVv09wJhDznWuX35FkcGuw83e+u+Ce9LHxusy1eA=; b=U37pl3erfIEdq2beKqERbSPZsM5L/uSCOfiiJrYMu348ck+zRNyvURau oPD/S7EIE+nYjjaSosvwbqxqoXHM66JH/G49PHz1tROWGXXFjsws+SZcv h359FWifPIfAeDplVQE/KrYSMeBqXFqx4KWUaXFCWoECmCJaa0xFlbCOO yYddSmg1kuQlgNET7r+RGwl/snVGHA0gQUYWffR9qE8HoYK1MQuCfBazH mRjcFQSiC9WFf3hPdx+22D/89VTkqqhq7M8INxoloGLgeQ5gT7QpmI390 bZMKArqA+b+gul8MLUdQmzbcnmrAcKGMEUPmqhyMHf3bhcKWjrdcSi5r7 g==; X-CSE-ConnectionGUID: LgO7xaTOS1WTLU9RdewdUQ== X-CSE-MsgGUID: pPhu9msoQ8CEkXubE+OoQA== X-IronPort-AV: E=McAfee;i="6700,10204,11325"; a="37974477" X-IronPort-AV: E=Sophos;i="6.13,231,1732608000"; d="scan'208";a="37974477" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Jan 2025 08:23:21 -0800 X-CSE-ConnectionGUID: Gs42ioSTTdiI6rvaxlfPEg== X-CSE-MsgGUID: xn+7imiORgumO1Dixj5oOQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,224,1728975600"; d="scan'208";a="112438539" Received: from unknown (HELO [10.247.119.253]) ([10.247.119.253]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Jan 2025 08:23:12 -0800 Message-ID: <81714cba-7924-4a4a-a5fc-b6f84bda352a@intel.com> Date: Fri, 24 Jan 2025 08:23:09 -0800 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/3] selftests/lam: Skip test if LAM is disabled To: Maciej Wieczor-Retman , shuah@kernel.org, hpa@zytor.com, x86@kernel.org, dave.hansen@linux.intel.com, bp@alien8.de, mingo@redhat.com, tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kirill@shutemov.name, "Kirill A. Shutemov" , Shuah Khan References: <09e6958c424a5da763f2331745cfe145962b0a83.1732728879.git.maciej.wieczor-retman@intel.com> Content-Language: en-US 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: <09e6958c424a5da763f2331745cfe145962b0a83.1732728879.git.maciej.wieczor-retman@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/27/24 09:35, Maciej Wieczor-Retman wrote: > +static inline int kernel_has_lam(void) > +{ > + unsigned long bits; > + > + syscall(SYS_arch_prctl, ARCH_GET_MAX_TAG_BITS, &bits); > + return !!bits; > +} Generally, I'm less picky about selftest/ code than in-kernel code. But people really do take selftest code and use it as a starting point for production code. I'd much rather have overly verbose, obviously correct code: err = syscall(SYS_arch_prctl, ARCH_GET_MAX_TAG_BITS, &bits); /* Handle syscall failure, like pre-LAM kernels: */ if (err) return 0 /* Tag bits are empty on non-LAM systems: */ return !!bits; Actually, I was going to argue for that^ just on style and writing good code. But then I spotted a bug. What happens if the kernel has CONFIG_ADDRESS_MASKING=n, either because it is config'd off or it's old? The: put_user(0, (unsigned long __user *)arg2); won't ever get run and 'bits' will be uninitialized. So, I think this code was trying to be compact, fast and clever. But it really just turns out to be buggy.