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Thu, 10 Oct 2019 09:47:56 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9A9hESJ162338; Thu, 10 Oct 2019 09:47:56 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3020.oracle.com with ESMTP id 2vh5ccu4ec-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 10 Oct 2019 09:47:55 +0000 Received: from abhmp0005.oracle.com (abhmp0005.oracle.com [141.146.116.11]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x9A9lpL5004016; Thu, 10 Oct 2019 09:47:51 GMT Received: from tomti.i.net-space.pl (/10.175.215.43) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 10 Oct 2019 02:47:50 -0700 Date: Thu, 10 Oct 2019 11:43:49 +0200 From: Daniel Kiper To: Randy Dunlap Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org, 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 Subject: Re: [PATCH v3 1/3] x86/boot: Introduce the kernel_info Message-ID: <20191010094349.la3sjiuiikmegjck@tomti.i.net-space.pl> References: <20191009105358.32256-1-daniel.kiper@oracle.com> <20191009105358.32256-2-daniel.kiper@oracle.com> <181249b6-5833-6f29-7d38-6dacc3f8ee62@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <181249b6-5833-6f29-7d38-6dacc3f8ee62@infradead.org> User-Agent: NeoMutt/20170113 (1.7.2) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9405 signatures=668684 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910100087 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9405 signatures=668684 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910100087 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 09, 2019 at 05:43:31PM -0700, Randy Dunlap wrote: > 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? s/It/The kernel_info structure/ Is it better? > > + 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/ OK. > > +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? EsTT == Example STrucT EsTs == Example STringS Anyway, it can be anything which does not collide with existing variable length data magics. There are none right now. So, it can be anything. Maybe I should add something saying that. Daniel