From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7827EC47404 for ; Thu, 10 Oct 2019 00:44:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A9CA20B7C for ; Thu, 10 Oct 2019 00:44:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="l8g4s4ed" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732604AbfJJAoJ (ORCPT ); Wed, 9 Oct 2019 20:44:09 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:50502 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731553AbfJJAoI (ORCPT ); Wed, 9 Oct 2019 20:44:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To: Subject:Sender:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=50od/B3PK0CJO1ZT1qu05XYWV3Ldcc+kIxtp//OtB+E=; b=l8g4s4edagE05Kh3Sqcy98sH/ gqt8BJzo0AvezCil0cCxfu/nx/SPgwTNbirqwkXY8R3Bytw6iwSB/OnGeJ+wqIUm/KRszl5rreync a1pTNC/xuTjMuDTU1PjRRP5L2zheXEFBeTJ222Rm3U4uVaTMTziHaI3cvZkeNekDOMam+0au0EcCp pAwJFZEqGuZlrFqxUSVPJ9eD3Zqtsh4qAsIe6tyYul6B8holW4Q+Y4xEGStBngYYpw3SsQnKYpACI PpHpLMRnvH530lUGesEr3FJg5n45i/MHelHXF3oTJtvD0yPbhkLZziAkkA2SVcNwRYAEi0wj29cFX i1TviFx+Q==; Received: from [2601:1c0:6280:3f0::9ef4] by bombadil.infradead.org with esmtpsa (Exim 4.92.2 #3 (Red Hat Linux)) id 1iIMYG-0002Wz-Q9; Thu, 10 Oct 2019 00:43:32 +0000 Subject: Re: [PATCH v3 1/3] x86/boot: Introduce the kernel_info To: Daniel Kiper , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org Cc: ard.biesheuvel@linaro.org, boris.ostrovsky@oracle.com, bp@alien8.de, corbet@lwn.net, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, eric.snowberg@oracle.com, hpa@zytor.com, jgross@suse.com, konrad.wilk@oracle.com, mingo@redhat.com, ross.philipson@oracle.com, tglx@linutronix.de References: <20191009105358.32256-1-daniel.kiper@oracle.com> <20191009105358.32256-2-daniel.kiper@oracle.com> From: Randy Dunlap Message-ID: <181249b6-5833-6f29-7d38-6dacc3f8ee62@infradead.org> Date: Wed, 9 Oct 2019 17:43:31 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191009105358.32256-2-daniel.kiper@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Questions and comments below... Thanks. On 10/9/19 3:53 AM, Daniel Kiper wrote: > Suggested-by: H. Peter Anvin > Signed-off-by: Daniel Kiper > Reviewed-by: Konrad Rzeszutek Wilk > Reviewed-by: Ross Philipson > --- > --- > Documentation/x86/boot.rst | 121 +++++++++++++++++++++++++++++++++ > arch/x86/boot/Makefile | 2 +- > arch/x86/boot/compressed/Makefile | 4 +- > arch/x86/boot/compressed/kernel_info.S | 17 +++++ > arch/x86/boot/header.S | 1 + > arch/x86/boot/tools/build.c | 5 ++ > arch/x86/include/uapi/asm/bootparam.h | 1 + > 7 files changed, 148 insertions(+), 3 deletions(-) > create mode 100644 arch/x86/boot/compressed/kernel_info.S > > diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst > index 08a2f100c0e6..d5323a39f5e3 100644 > --- a/Documentation/x86/boot.rst > +++ b/Documentation/x86/boot.rst > @@ -68,8 +68,25 @@ Protocol 2.12 (Kernel 3.8) Added the xloadflags field and extension fields > Protocol 2.13 (Kernel 3.14) Support 32- and 64-bit flags being set in > xloadflags to support booting a 64-bit kernel from 32-bit > EFI > + > +Protocol 2.14: BURNT BY INCORRECT COMMIT ae7e1238e68f2a472a125673ab506d49158c1889 > + (x86/boot: Add ACPI RSDP address to setup_header) > + DO NOT USE!!! ASSUME SAME AS 2.13. > + > +Protocol 2.15: (Kernel 5.5) Added the kernel_info. > ============= ============================================================ > > +.. note:: > + The protocol version number should be changed only if the setup header > + is changed. There is no need to update the version number if boot_params > + or kernel_info are changed. Additionally, it is recommended to use > + xloadflags (in this case the protocol version number should not be > + updated either) or kernel_info to communicate supported Linux kernel > + features to the boot loader. Due to very limited space available in > + the original setup header every update to it should be considered > + with great care. Starting from the protocol 2.15 the primary way to > + communicate things to the boot loader is the kernel_info. > + > > Memory Layout > ============= > @@ -207,6 +224,7 @@ Offset/Size Proto Name Meaning > 0258/8 2.10+ pref_address Preferred loading address > 0260/4 2.10+ init_size Linear memory required during initialization > 0264/4 2.11+ handover_offset Offset of handover entry point > +0268/4 2.15+ kernel_info_offset Offset of the kernel_info > =========== ======== ===================== ============================================ > > .. note:: > @@ -855,6 +873,109 @@ Offset/size: 0x264/4 > > See EFI HANDOVER PROTOCOL below for more details. > > +============ ================== > +Field name: kernel_info_offset > +Type: read > +Offset/size: 0x268/4 > +Protocol: 2.15+ > +============ ================== > + > + This field is the offset from the beginning of the kernel image to the > + kernel_info. It is embedded in the Linux image in the uncompressed ^^ What does It refer to, please? > + protected mode region. > + > + > +The kernel_info > +=============== > + > +The relationships between the headers are analogous to the various data > +sections: > + > + setup_header = .data > + boot_params/setup_data = .bss > + > +What is missing from the above list? That's right: > + > + kernel_info = .rodata > + > +We have been (ab)using .data for things that could go into .rodata or .bss for > +a long time, for lack of alternatives and -- especially early on -- inertia. > +Also, the BIOS stub is responsible for creating boot_params, so it isn't > +available to a BIOS-based loader (setup_data is, though). > + > +setup_header is permanently limited to 144 bytes due to the reach of the > +2-byte jump field, which doubles as a length field for the structure, combined > +with the size of the "hole" in struct boot_params that a protected-mode loader > +or the BIOS stub has to copy it into. It is currently 119 bytes long, which > +leaves us with 25 very precious bytes. This isn't something that can be fixed > +without revising the boot protocol entirely, breaking backwards compatibility. > + > +boot_params proper is limited to 4096 bytes, but can be arbitrarily extended > +by adding setup_data entries. It cannot be used to communicate properties of > +the kernel image, because it is .bss and has no image-provided content. > + > +kernel_info solves this by providing an extensible place for information about > +the kernel image. It is readonly, because the kernel cannot rely on a > +bootloader copying its contents anywhere, but that is OK; if it becomes > +necessary it can still contain data items that an enabled bootloader would be > +expected to copy into a setup_data chunk. > + > +All kernel_info data should be part of this structure. Fixed size data have to > +be put before kernel_info_var_len_data label. Variable size data have to be put > +behind kernel_info_var_len_data label. Each chunk of variable size data has to s/behind/after/ > +be prefixed with header/magic and its size, e.g.: > + > + kernel_info: > + .ascii "LToP" /* Header, Linux top (structure). */ > + .long kernel_info_var_len_data - kernel_info > + .long kernel_info_end - kernel_info > + .long 0x01234567 /* Some fixed size data for the bootloaders. */ > + kernel_info_var_len_data: > + example_struct: /* Some variable size data for the bootloaders. */ > + .ascii "EsTT" /* Header/Magic. */ > + .long example_struct_end - example_struct > + .ascii "Struct" > + .long 0x89012345 > + example_struct_end: > + example_strings: /* Some variable size data for the bootloaders. */ > + .ascii "EsTs" /* Header/Magic. */ Where do the Magic values "EsTT" and "EsTs" come from? where are they defined? > + .long example_strings_end - example_strings > + .asciz "String_0" > + .asciz "String_1" > + example_strings_end: > + kernel_info_end: > + > +This way the kernel_info is self-contained blob. > + > + > +Details of the kernel_info Fields > +================================= > + > +============ ======== > +Field name: header > +Offset/size: 0x0000/4 > +============ ======== > + > + Contains the magic number "LToP" (0x506f544c). > + > +============ ======== > +Field name: size > +Offset/size: 0x0004/4 > +============ ======== > + > + This field contains the size of the kernel_info including kernel_info.header. > + It does not count kernel_info.kernel_info_var_len_data size. This field should be > + used by the bootloaders to detect supported fixed size fields in the kernel_info > + and beginning of kernel_info.kernel_info_var_len_data. > + > +============ ======== > +Field name: size_total > +Offset/size: 0x0008/4 > +============ ======== > + > + This field contains the size of the kernel_info including kernel_info.header > + and kernel_info.kernel_info_var_len_data. > + > > The Image Checksum > ================== -- ~Randy