From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id DB0C17D082 for ; Wed, 10 Oct 2018 06:39:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725864AbeJJOA0 (ORCPT ); Wed, 10 Oct 2018 10:00:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:50674 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725791AbeJJOA0 (ORCPT ); Wed, 10 Oct 2018 10:00:26 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id D9FC4ACAB; Wed, 10 Oct 2018 06:39:43 +0000 (UTC) Subject: Re: [PATCH v5 0/3] x86: make rsdp address accessible via boot params To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, linux-doc@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, corbet@lwn.net, boris.ostrovsky@oracle.com, Peter Zijlstra , Kees Cook References: <20181010061456.22238-1-jgross@suse.com> <20181010062352.GC37224@gmail.com> From: Juergen Gross Openpgp: preference=signencrypt Autocrypt: addr=jgross@suse.com; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb Message-ID: <12afa65a-9e07-bb2c-5621-85074ea37135@suse.com> Date: Wed, 10 Oct 2018 08:39:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181010062352.GC37224@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 10/10/2018 08:23, Ingo Molnar wrote: > > * Juergen Gross wrote: > >> In the non-EFI boot path the ACPI RSDP table is currently found via >> either EBDA or by searching through low memory for the RSDP magic. >> This requires the RSDP to be located in the first 1MB of physical >> memory. Xen PVH guests, however, get the RSDP address via the start of >> day information block. >> >> In order to support an arbitrary RSDP address this patch series adds >> the physical address of the RSDP to the boot params structure filled >> by the boot loader. >> >> Juergen Gross (3): >> x86/xen: fix boot loader version reported for pvh guests >> x86/boot: add acpi rsdp address to setup_header >> x86/acpi: take rsdp address for boot params if available >> >> Documentation/x86/boot.txt | 32 +++++++++++++++++++++++++++++++- >> arch/x86/boot/header.S | 6 +++++- >> arch/x86/include/asm/acpi.h | 7 +++++++ >> arch/x86/include/asm/x86_init.h | 2 ++ >> arch/x86/include/uapi/asm/bootparam.h | 4 ++++ >> arch/x86/kernel/acpi/boot.c | 6 ++++++ >> arch/x86/kernel/head32.c | 1 + >> arch/x86/kernel/head64.c | 2 ++ >> arch/x86/kernel/setup.c | 17 +++++++++++++++++ >> arch/x86/kernel/x86_init.c | 3 +-- >> arch/x86/xen/enlighten_pvh.c | 2 +- >> 11 files changed, 77 insertions(+), 5 deletions(-) > > I have some vague memories of an older variant of this feature breaking stuff and resulting in > me involuntarily participating in an overly long bisection session. > > If that memory is right and I'm not confusing it with some other patchset, could you please > provide some more context, what that old problem was, how it was resolved, whether it is > expected to trigger on any machines, etc., to create some warm fuzzy feelings about this > patch-set and to reduce my bisectofobia? ;-) You can just dive into the discussion we had back in February: https://lore.kernel.org/lkml/20180213163244.j2zuxyhs4kbfhwgj@gmail.com/ The scheme I have used in V5 of the series is the one you agreed to use back then. A quick summary of the problem you mentioned: There are some downstream variants of grub2 with a patch breaking the boot protocol by writing garbage past the end of setup_header. Adding a new field at the end of setup_header (here: rsdp_address) resulted in those grub2 variants clobbering the preset value of 0. The solution is to let grub2 report back the used boot protocol version with setting a flag "I am reporting back my version". The kernel now is capable to know which fields of setup_header are known to grub2 and can act accordingly. The related grub2 patch series is under review right now. Juergen