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Tue, 06 Oct 2026 11:02:25 -0700 (PDT) X-Received: by 2002:a05:600c:1c16:b0:4a1:7832:dfd6 with SMTP id 5b1f17b1804b1-4a17b5340c8mr40388535e9.5.1791309744934; Tue, 06 Oct 2026 11:02:24 -0700 (PDT) Received: from px13 ([2a06:5902:822:4600:6f35:9ac4:c6c9:f701]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a17f493761sm5540315e9.2.2026.10.06.11.02.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Oct 2026 11:02:24 -0700 (PDT) Date: Tue, 6 Oct 2026 19:02:22 +0100 From: Chris Bainbridge To: Mike Rapoport Cc: Pasha Tatashin , Jason Miu , Pratyush Yadav , Alexander Graf , Ran Xiaokai , regressions@lists.linux.dev, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org Subject: Re: [BUG] KHO handover hangs when memmap reserves PMEM Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@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: On Tue, Oct 06, 2026 at 12:55:31PM +0200, Mike Rapoport wrote: > On Sat, Oct 03, 2026 at 06:02:27PM +0100, Chris Bainbridge wrote: > > Hello, > > > > I am reporting a regression in KHO handover. > > > > In the most recent Ubuntu 26.10 beta mini-ISO releases (2026-09-18 onwards), > > the first kernel reserves RAM for the downloaded ISO with a memmap directive > > such as memmap=!4G, then kexecs a second kernel. On affected kernels, the > > first kernel reaches "kexec_core: Starting new kernel", but the second kernel > > produces no further output and QEMU spins at 100% CPU. On unaffected kernels, > > the second kernel starts and finds /dev/pmem0 with the expected "Persistent > > Memory (legacy)" range in /proc/iomem. > > TO make sure I understand this correctly, you enable KHO in the builds of > the installer kernel and then the installer command line explicitly enables > KHO. Yes. > Is there anything you actually preserve with KHO when kexec'ing the second > kernel? No. kho=off is a valid workaround for the mini ISO. I only reported it as a regression here because this was working until the bisected commit was merged. If this is intended behaviour then it is not a problem.