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Peter Anvin" , Peter Zijlstra , Pratyush Yadav , Rob Herring , Rob Herring , Saravana Kannan , Stanislav Kinsburskii , Steven Rostedt , Thomas Gleixner , Tom Lendacky , Usama Arif , Will Deacon , devicetree@vger.kernel.org, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, Philipp Rudo , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , linux-s390@vger.kernel.org Subject: Re: [PATCH v4 00/14] kexec: introduce Kexec HandOver (KHO) Message-ID: References: <20250206132754.2596694-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 02CmlzRAvH6gUhNjDul_d5grRXN4j5Cf X-Proofpoint-GUID: vqtrf0KyRdj5sNl93G5J7u-LcnzQFqNz X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-20_07,2025-02-20_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 suspectscore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=660 bulkscore=0 phishscore=0 malwarescore=0 mlxscore=0 adultscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2502200116 On Thu, Feb 20, 2025 at 09:49:52AM +0800, Dave Young wrote: > On Wed, 19 Feb 2025 at 21:55, Alexander Graf wrote: > > >>> What architecture exactly does this KHO work fine? Device Tree > > >>> should be ok on arm*, x86 and power*, but how about s390? > > >> KHO does not use device tree as the boot protocol, it uses FDT as a data > > >> structure and adds architecture specific bits to the boot structures to > > >> point to that data, very similar to how IMA_KEXEC works. > > >> > > >> Currently KHO is implemented on arm64 and x86, but there is no fundamental > > >> reason why it wouldn't work on any architecture that supports kexec. > > > Well, the problem is whether there is a way to add dtb in the early > > > boot path, for X86 it is added via setup_data, if there is no such > > > way I'm not sure if it is doable especially for passing some info for > > > early boot use. Then the KHO will be only for limited use cases. > > > > > > Every architecture has a platform specific way of passing data into the > > kernel so it can find its command line and initrd. S390x for example has > > struct parmarea. To enable s390x, you would remove some of its padding > > and replace it with a KHO base addr + size, so that the new kernel can > > find the KHO state tree. > > Ok, thanks for the info, I cced s390 people maybe they can provide inputs. If I understand correctly, the parmarea would be used for passing the FDT address - which appears to be fine. However, s390 does not implement early_memremap()/early_memunmap(), which KHO needs. Thanks, Dave!