From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.9]) (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 124D4128831 for ; Fri, 23 Feb 2024 19:08:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.9 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708715303; cv=none; b=CoJjopS4/6xEts3Emc1KbSxF5WtPt2jg+GsTLRILmTp0gyXySRW5EQqjDb6UP4Um92jsfQSrY70ugSj85pXq2kPDpGXbXXO3IJljHHJxcLWdksiBUrREC4T9sboztWX4DAj9/nej6C0SjPavJjlPYTkKfFLOdC9sbMjsbr3QlcU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708715303; c=relaxed/simple; bh=7R9RCGEfnv7As+Ov4XdPpDS7BmdZlFCHr3jRKeBO7MA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=O2si8Ln418i19lJNuYxNM8xgnepylF0U+Uo8A3KmvxO+O/WM2pr+6qCsOQDG9Eqs7LCBdDIjgdUYVdOmz/HI+nfRF8L3jkvQVJx00Rp1xdQTBpexKhOLKlIc9T1chgogo5so9Glq5rVnB/Ghe1mECmX9++bZYokpTtrKKFMD26g= 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=TVaOOIAU; arc=none smtp.client-ip=192.198.163.9 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="TVaOOIAU" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1708715301; x=1740251301; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=7R9RCGEfnv7As+Ov4XdPpDS7BmdZlFCHr3jRKeBO7MA=; b=TVaOOIAU+238cg/9AN1eGMPi+SRQn4iWX7W6uODZXoqBUwtwg8y9LXXe m/pruRBj7CHMAByyy7WAJK02wwdlYkKYQkgHfkGRJ9cUCvmyInu6qpzfm egDXAJ8jq9AiXAHEKd/vJ3aAlGvxcPURxQo+Yh5R0BHCbxsOvv5mCIHJn bmw/zw8wpzrNs9Edn17eu0j4p3Y12uCUey1ndssmRvdO79RkBEd7BLAHx hqMyZkN4CGYMwzkBe4chexQFp5NdT6SZ79DifrP2VYJPuag6RdJ7YAD8r gemqesVwz4XXfBnbf80pfIuhHwQec2h8uzl4iVozSzUI2ag9FANRCsmRt g==; X-IronPort-AV: E=McAfee;i="6600,9927,10993"; a="13746755" X-IronPort-AV: E=Sophos;i="6.06,180,1705392000"; d="scan'208";a="13746755" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Feb 2024 11:08:20 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,180,1705392000"; d="scan'208";a="5979122" Received: from gtkramer-mobl1.amr.corp.intel.com (HELO [10.209.82.163]) ([10.209.82.163]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Feb 2024 11:08:20 -0800 Message-ID: Date: Fri, 23 Feb 2024 11:08:18 -0800 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: [PATCHv7 08/16] x86/tdx: Account shared memory Content-Language: en-US To: "Kirill A. Shutemov" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org Cc: "Rafael J. Wysocki" , Peter Zijlstra , Adrian Hunter , Kuppuswamy Sathyanarayanan , Elena Reshetova , Jun Nakajima , Rick Edgecombe , Tom Lendacky , "Kalra, Ashish" , Sean Christopherson , "Huang, Kai" , Baoquan He , kexec@lists.infradead.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org References: <20240212104448.2589568-1-kirill.shutemov@linux.intel.com> <20240212104448.2589568-9-kirill.shutemov@linux.intel.com> 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: <20240212104448.2589568-9-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/12/24 02:44, Kirill A. Shutemov wrote: > The kernel will convert all shared memory back to private during kexec. > The direct mapping page tables will provide information on which memory > is shared. > > It is extremely important to convert all shared memory. If a page is > missed, it will cause the second kernel to crash when it accesses it. > > Keep track of the number of shared pages. This will allow for > cross-checking against the shared information in the direct mapping and > reporting if the shared bit is lost. > > Include a debugfs interface that allows for the check to be performed at > any point. When I read this, I thought you were going to do some automatic checking. Could you make it more clear here that it's 100% up to the user to figure out if the numbers in debugfs match and whether there's a problem? This would also be a great place to mention that the whole thing is racy. > +static atomic_long_t nr_shared; > + > +static inline bool pte_decrypted(pte_t pte) > +{ > + return cc_mkdec(pte_val(pte)) == pte_val(pte); > +} Name this pte_is_decrypted(), please. > /* Called from __tdx_hypercall() for unrecoverable failure */ > noinstr void __noreturn __tdx_hypercall_failed(void) > { > @@ -821,6 +829,11 @@ static int tdx_enc_status_change_finish(unsigned long vaddr, int numpages, > if (!enc && !tdx_enc_status_changed(vaddr, numpages, enc)) > return -EIO; > > + if (enc) > + atomic_long_sub(numpages, &nr_shared); > + else > + atomic_long_add(numpages, &nr_shared); > + > return 0; > } > > @@ -896,3 +909,59 @@ void __init tdx_early_init(void) > > pr_info("Guest detected\n"); > } > + > +#ifdef CONFIG_DEBUG_FS > +static int tdx_shared_memory_show(struct seq_file *m, void *p) > +{ > + unsigned long addr, end; > + unsigned long found = 0; > + > + addr = PAGE_OFFSET; > + end = PAGE_OFFSET + get_max_mapped(); > + > + while (addr < end) { > + unsigned long size; > + unsigned int level; > + pte_t *pte; > + > + pte = lookup_address(addr, &level); > + size = page_level_size(level); > + > + if (pte && pte_decrypted(*pte)) > + found += size / PAGE_SIZE; > + > + addr += size; > + > + cond_resched(); > + } This is totally racy, right? Nothing prevents the PTE from flip-flopping all over the place. > + seq_printf(m, "Number of shared pages in kernel page tables: %16lu\n", > + found); > + seq_printf(m, "Number of pages accounted as shared: %16ld\n", > + atomic_long_read(&nr_shared)); > + return 0; > +} Ditto with 'nr_shared'. There's nothing to say that the page table walk has anything to do with 'nr_shared' by the time we get down here. That's not _fatal_ for a debug interface, but the pitfalls need to at least be discussed. Better yet would be to make sure this and the cpa code don't stomp on each other.