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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: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 44k4kpuuz3aqzobq1hsmzufg51jttodz X-Rspam-User: X-Rspamd-Queue-Id: AF02A10000B X-Rspamd-Server: rspam08 X-HE-Tag: 1791309747-419802 X-HE-Meta: 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 TwEGR5oU f1aBbFSTVXI+ReRoWjZZ0xYy9dw/d3J275qiVi3/Jo2el1Wf/BgKZaRJWmB332xcChiE2JbnW+80sL7dBLsCR6xsWax9XmkwvLOVQW5RYV5xEkWi5MCvD6COxihasHw8g7c9GYHdlZtGCfawYOpxu9KTO16SNgVaKHaDI0EzIm/roqxDSjtw7NZ/0M+dzgT8n6zO6AzZ9yqFog0SKLEc7mus58W9nNwiNDjFtFOTdHuBO0cDo7iXpCbkAWbQKv6XaN26ht//qKdAJXXddnxkMHhNJ2RF0OmqjFu90VZ/ZMbtow2XVLAQ0ra3zSeNd8OsfGHkS8Q35M8T5AoWLpjyiI7rvtRwcrxqfQdTipLeyAqq6BHoShp05LsIRxSBqGC0uOCZYQQKa1yCYw7IzbAFvaMej6kr0s4otqBAV Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.