From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (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 D05B2347BCE for ; Fri, 24 Oct 2025 18:02:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761328973; cv=none; b=ekPr9ZmqFGApaWypyRO5LF8DOH3EezOgxYBtTIasMMzYp27BNO2JlDYW4i9OJz3xSEigSWEUTbmVYw+snBBapdS++ofrYvmG/2mIm09vTJZmlUtOofgkmqdU+AKTu6iF6KgsYrhOSxA0Nlqcg5FykJFk5rJ1Uvm8UH4ZHfxiZY4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761328973; c=relaxed/simple; bh=v7jjhQRygi54OOkAexn7Ztbxj0wNCzmMN4Xosb7Acro=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JL1gm8uC5OM0w9rsbgl5LfGqHWo5RXi4u5L8MDpak/Zn4YsYieGsQhg0pALODNOAT2OUu+cp68m5pxlGVo+6pgp/eYIyr7o3vehrr5JpRK4Xmvfnfszc9SQgLL1RAt7Sq4HY8ZR1stWpwD79Gu1mbQ21CheJxENjOAMXXfcK9UI= 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=WKJKTOYQ; arc=none smtp.client-ip=192.198.163.10 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="WKJKTOYQ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1761328972; x=1792864972; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=v7jjhQRygi54OOkAexn7Ztbxj0wNCzmMN4Xosb7Acro=; b=WKJKTOYQWVc+L+FHiQ2c1B3Iq8afevitBtGtvOA33D/Vbd/dbXDxUacC 4IV6iWgGQ77jxE77UjL/eeW7JwhMCNz2fEytyoXZ7XtGrnn9F1LOXQS8d xxAITTsuXzlTwzIEKN/hM9gyeoe94TK5HlgkqR0DbvGM4OltMZwVdPedt 1POem7dz6v2GkNRtKn2nh+XKPTnUfWcyfAuiC4zx9kva67+8bn23g6V/v wQl/73YlfeWju2GfhAfpRLEj6g0RVUhFgrO4bezDqHvlx2fZNKJ72DZFr acXSfZkXy1go/1jn7ttkIdX5K1R2YWe2ZHkToL74zG9hrvXW34fJPSmoH w==; X-CSE-ConnectionGUID: 8RpxnzS8Q6+YdX2fz0ySUw== X-CSE-MsgGUID: jj/VXrn/Rnujvzl9gP+d+g== X-IronPort-AV: E=McAfee;i="6800,10657,11586"; a="74860527" X-IronPort-AV: E=Sophos;i="6.19,253,1754982000"; d="scan'208";a="74860527" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Oct 2025 11:02:50 -0700 X-CSE-ConnectionGUID: pQqplbAiRlWiBqLu7iy8ZA== X-CSE-MsgGUID: Jg7yDgbLSkatZYMLTE/4aQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,253,1754982000"; d="scan'208";a="188784768" Received: from aschofie-mobl2.amr.corp.intel.com (HELO [10.125.109.44]) ([10.125.109.44]) by orviesa004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Oct 2025 11:02:50 -0700 Message-ID: Date: Fri, 24 Oct 2025 11:02:49 -0700 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 00/21] Runtime TDX Module update support To: Chao Gao Cc: Vishal Annapurve , "Reshetova, Elena" , "linux-coco@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "Chatre, Reinette" , "Weiny, Ira" , "Huang, Kai" , "Williams, Dan J" , "yilun.xu@linux.intel.com" , "sagis@google.com" , "paulmck@kernel.org" , "nik.borisov@suse.com" , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , "Kirill A. Shutemov" , Paolo Bonzini , "Edgecombe, Rick P" , Thomas Gleixner References: <5b4c2bb3-cfde-4559-a59d-0ff9f2a250b4@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/24/25 00:43, Chao Gao wrote: ... > Beyond "the kvm_tdx object gets torn down during a build," I see two potential > issues: > > 1. TD Build and TDX migration aren't purely kernel processes -- they span multiple > KVM ioctls. Holding a read-write lock throughout the entire process would > require exiting to userspace while the lock is held. I think this is > irregular, but I'm not sure if it's acceptable for read-write semaphores. Sure, I guess it's irregular. But look at it this way: let's say we concocted some scheme to use a TD build refcount and a module update flag, had them both wait_event_interruptible() on each other, and then did wakeups. That would get the same semantics without an rwsem. So is your issue with the rwsem, or the idea that one bit of userspace can block another bit of userspace from doing something for arbitrary lengths of time? The one thing that worries me is solidly tying the build-side down_read() to the lifetime of kvm_tdx. But that shouldn't be rocket science. There also isn't a down_write_interruptible(), only down_write_killable(). > 2. The kernel may need to hold this read-write lock for operations not yet > defined in the future. The TDX Module Base spec [*] notes on page 55: > > : Future TDX Module versions may have different or additional update-sensitive > : cases. By design, such cases apply to a small portion of the overall TD > : lifecycle. Sure... But that's not a license for the TDX module to do completely silly things. Elena is on cc here for a reason and I'm sure she'll ensure that nothing silly gets put into the TDX module that will cause problems here.