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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 75408C3A5A3 for ; Tue, 27 Aug 2019 08:15:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 433B6206BF for ; Tue, 27 Aug 2019 08:15:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566893749; bh=5hngcFTxsbfc5fjmAjHazMNmqRY0AOYp4ApyDHXH/Cg=; h=Subject:To:Cc:References:From:Date:In-Reply-To:List-ID:From; b=n0m514oTxoyW4zRq6/T9p/cx8/UM6UGEF8ehn6Eh2VPFtY7IFJ12k4LjWW/uyt1Pp 7dzneZVT4qtng0FevDlRLNDpoyFLtAK9I9IMB8FaV/gGcSOVxK24kJOqIEr26BhoAQ pdo4gcD9Q8zjnBczavje0wjDdPVcU6K/XdjKgNBs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730263AbfH0IPs (ORCPT ); Tue, 27 Aug 2019 04:15:48 -0400 Received: from foss.arm.com ([217.140.110.172]:40584 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729575AbfH0IPq (ORCPT ); Tue, 27 Aug 2019 04:15:46 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A6A82337; Tue, 27 Aug 2019 01:15:45 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 61C483F246; Tue, 27 Aug 2019 01:15:44 -0700 (PDT) Subject: Re: [PATCH v1 0/6] Allow kexec reboot for GICv3 and device tree To: Pavel Tatashin Cc: James Morris , Sasha Levin , kexec mailing list , LKML , Linux ARM , James Morse , Vladimir Murzin , Mark Rutland References: <20190826190056.27854-1-pasha.tatashin@soleen.com> <20190826201313.246208e9@why> From: Marc Zyngier Organization: Approximate Message-ID: Date: Tue, 27 Aug 2019 09:15:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: 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 On 26/08/2019 22:25, Pavel Tatashin wrote: > On Mon, Aug 26, 2019 at 3:13 PM Marc Zyngier wrote: >> >> On Mon, 26 Aug 2019 15:00:50 -0400 >> Pavel Tatashin wrote: >> >>> Marc Zyngier added the support for kexec and GICv3 for EFI based systems. >>> However, it is still not possible todo on systems with device trees. >>> >>> Here is EFI fixes from Marc: >>> https://lore.kernel.org/lkml/20180921195954.21574-1-marc.zyngier@arm.com >>> >>> For Device Tree variant: lets allow reserve a memory region in interrupt >>> controller node, and use this property to allocate interrupt tables. >> >> There is no such thing as a "device tree variant". As long as your >> bootloader implements EFI, everything will work correctly, whether >> you're using DT, ACPI, or the anything else. >> >> This already works today, without any need to add anything to the >> kernel (I have systems using EDK II and u-boot, both implementing EFI, >> and I'm able to kexec without any issue). If your bootloader doesn't >> support EFI, here's a good opportunity to implement it! > > Hi Marc, > > Thank you very much for looking at this work. > > Running Linux without EFI is common, and there are scenarios which > make it appropriate. As I understand most of embedded linux do not > have EFI enabled, and thus I do not see a reason why we would not > support a first class feature of Linux (kexec) on non-EFI bootloaders. Define "most". All the arm64 systems I have around (and trust me, that's quite a number of them) can either use u-boot, which has more than enough EFI support to use this functionality, or use EDK-II natively. > We (Microsoft) have a small highly secure device with a high uptime > requirement. The device also has PCIe and thus GICv3. The update for PCIe doesn't imply GICv3 at all. > this device relies on kexec. For a number of reasons, it was decided > to use U-Boot and Linux without EFI enabled. One of those reasons is > to improve boot performance, enabling EFI in U-Boot alone reduces the > boot performance by half a second. Our total reboot budget is under a > second which makes that half a second unacceptable. Also, adding EFI > support to kernel increases its size and there are security > implications from enabling more code both in U-Boot and Linux. You're are missing the point. kexec with EFI has 0 overhead (no non-kernel EFI code gets executed), doesn't impact your time budget, and only relies on a single in-memory table. This can be pretty trivially provided by the dumbest EFI shim. All you are describing above is a set of self imposed limitations in your bootloader, which you are fully in control of. So instead of reinventing a square wheel, I suggest you adopt the existing implementation. Another reason not to do this is interoperability: I want to be able to kexec whatever Linux kernel I want, without having to cope with all flavours of the same functionality. Effectively, the EFI table is a private ABI between two Linux kernels. We're not changing it. M. -- Jazz is not dead, it just smells funny...