From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by lists.ozlabs.org (Postfix) with ESMTP id 3rqDFg400PzDqKn for ; Wed, 13 Jul 2016 19:35:03 +1000 (AEST) Date: Wed, 13 Jul 2016 10:34:47 +0100 From: Mark Rutland To: Dave Young Cc: Arnd Bergmann , bhe@redhat.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Vivek Goyal , AKASHI Takahiro , "Eric W. Biederman" , bauerman@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Subject: Re: [RFC 0/3] extend kexec_file_load system call Message-ID: <20160713093432.GB14522@leverpostej> References: <20160712014201.11456-1-takahiro.akashi@linaro.org> <1911992.H2WpLRr2Fi@wuerfel> <20160712141810.GB30181@redhat.com> <293705810.hBL93OOmOz@wuerfel> <20160712145010.GA8447@leverpostej> <20160713023614.GB3222@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160713023614.GB3222@dhcp-128-65.nay.redhat.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Jul 13, 2016 at 10:36:14AM +0800, Dave Young wrote: > But consider we can kexec to a different kernel and a different initrd so there > will be use cases to pass a total different dtb as well. It depends on what you mean by "a different kernel", and what this implies for the DTB. I expect future arm64 Linux kernels to function with today's DTBs, and the existing boot protocol. The kexec_file_load syscall already has enough information for the kernel to inject the initrd and bootargs properties into a DTB. In practice on x86 today, kexec_file_load only supports booting to a Linux kernel, because the in-kernel purgatory only implements the x86 Linux boot protocol. Analagously, for arm64 I think that the first kernel should use its internal copy of the boot DTB, with /chosen fixed up appropriately, assuming the next kernel is an arm64 Linux image. If booting another OS, the only parts of the DTB I would expect to change are the properties under chosen, as everything else *should* be OS-independent. However the other OS may have a completely different boot protocol, might not even take a DTB, and will likely need a compeltely different purgatory implementation. So just allowing the DTB to be altered isn't sufficient for that case. There might be cases where we want a different DTB, but as far as I can tell we have nothing analagous on x86 today. If we do need this, we should have an idea of what real case(s) were trying to solve. Thanks, Mark.