From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.55.52.43]) (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 AA9A218EA1; Fri, 15 Dec 2023 22:05:11 +0000 (UTC) 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="cyl5T/AH" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1702677911; x=1734213911; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=C5u28TsTHMLf5q16FNbW/X5Am7vYw8OdDCzN+TJXAIg=; b=cyl5T/AHtQOO2AT82x4mrvIF5+Mg7MaKc5PKBVjykijQtuChAgTbj/Q3 FmjTHJEaD+OHM9SrHWV8Poyqm/CIN4Nu5EeD2i3roX4KThg+W/AExsObr am9dyoqMAo/0phYOqG8huAiHDLiw0nEEK0BQFdlnlJf5UrfT776om4WMD ApnrRks2zqf9PQFMjZWPqJCf+8v1uRD+zlzKxvSpyevxnfxzhxbE2Iwca FV9G2OA8HHHDao70FfC03Ct3kvVM5uRHsAWSm6bgMG85orI4Iocl2LNAF Dcc9QqyumvLC7l/JuP0UxitJwvDfuw2H5Z5pgjg40+q0TzPQ9dxItsn2E A==; X-IronPort-AV: E=McAfee;i="6600,9927,10925"; a="481520359" X-IronPort-AV: E=Sophos;i="6.04,280,1695711600"; d="scan'208";a="481520359" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 14:05:10 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10925"; a="803849500" X-IronPort-AV: E=Sophos;i="6.04,280,1695711600"; d="scan'208";a="803849500" Received: from jwaxmons-hp.amr.corp.intel.com (HELO [10.212.150.221]) ([10.212.150.221]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 14:05:10 -0800 Message-ID: Date: Fri, 15 Dec 2023 14:05:10 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] kexec: allocate kernel above bzImage's pref_address Content-Language: en-US To: Chris Koch Cc: Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-doc@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Cloud Hsu References: <20231215190521.3796022-1-chrisko@google.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 12/15/23 13:38, Chris Koch wrote: > On Fri, Dec 15, 2023 at 1:17 PM Dave Hansen wrote: ... >> Are you reporting a bug and is this a bug fix? It's not super clear >> from the changelog. > > I reported it as a bug yesterday in > https://lkml.org/lkml/2023/12/14/1529 -- I'm happy to reword this in > some way that indicates it's a bug fix. Ahh, thanks for the link! Please do include things like this as a "Link:" tag in the changelog (and use lore.kernel.org URLs when possible). >>> diff --git a/Documentation/arch/x86/boot.rst b/Documentation/arch/x86/boot.rst >>> index 22cc7a040dae..49bea8986620 100644 >>> --- a/Documentation/arch/x86/boot.rst >>> +++ b/Documentation/arch/x86/boot.rst >>> @@ -878,7 +878,8 @@ Protocol: 2.10+ >>> address if possible. >>> >>> A non-relocatable kernel will unconditionally move itself and to run >>> - at this address. >>> + at this address. A relocatable kernel will move itself to this address if it >>> + loaded below this address. >> >> I think we should avoid saying the same things over and over again in >> different spots. >> >> Here, it doesn't really help to enumerate the different interpretations >> of 'pref_address'. All that matters is that the bootloader can avoid >> the overhead of a later copy if it can place the kernel at >> 'pref_address'. The exact reasons that various kernels might decide to >> relocate are unimportant here. > > I think it's important documentation for bootloader authors. It's not > about avoiding overhead, it's about avoiding clobbering areas of > memory that may be reserved in e820 / EFI memory map, which the kernel > will do when it relocates itself to pref_address without checking > what's reserved and what's not. It emphasizes the importance of > choosing an address above pref_address. Happy to reword some way to > reflect that. Could we give this as a direction to bootloader authors? They should read 'pref_address' as a big, fat, "the kernel may blow this address away" message. ... >>> In normal kdump cases one does not have to set/change this option >>> as now bzImage can be compiled as a completely relocatable image >>> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c >>> index a61c12c01270..5dcd232d58bf 100644 >>> --- a/arch/x86/kernel/kexec-bzimage64.c >>> +++ b/arch/x86/kernel/kexec-bzimage64.c >>> @@ -498,7 +498,10 @@ static void *bzImage64_load(struct kimage *image, char *kernel, >>> kbuf.bufsz = kernel_len - kern16_size; >>> kbuf.memsz = PAGE_ALIGN(header->init_size); >>> kbuf.buf_align = header->kernel_alignment; >>> - kbuf.buf_min = MIN_KERNEL_LOAD_ADDR; >>> + if (header->pref_address < MIN_KERNEL_LOAD_ADDR) >>> + kbuf.buf_min = MIN_KERNEL_LOAD_ADDR; >>> + else >>> + kbuf.buf_min = header->pref_address; >>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN; >>> ret = kexec_add_buffer(&kbuf); >>> if (ret) >> >> Comment, please. >> >> It isn't clear from this hunk why or how this fixes the bug. How does >> this manage to avoid clobbering reserved areas? > > When allocated above pref_address, the kernel will not relocate itself > to an area that potentially overlaps with reserved memory. I'll add a > comment. Sounds good. > Not sure what the etiquette is on immediately sending a patch v2, or > waiting for more comments. I'll err on waiting on a couple more > comments before sending v2. Thanks for the review Please wait another few days.