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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E6CD9CA5FFF for ; Wed, 7 Oct 2026 06:12:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=SHTNYtREyl/jHXCf21L5IlTPz5bWxE9lwwBn75z0B7g=; b=b9VTEIWsteqi7CPilia/6qSL4m v+Egs69i+TuLQSsk8wx9OGcY/u7nlv458Gf56vJeAQJbDuGpQnS9LO/uZqDNvan+cB6aq+0ALibCo Y/9oltoEYo/a+NXiUUM6n+31JVvGcsxIx3wviq9lqEr8dkK7qdCj99TTCYJxfPFV3sTUDlU9RFl1L +/rvWVjHFmgoUaLp5IdHCoT4Rbvn3pO9MQ6aQ0axxX+ewHZOXLn5Ohaj6kkHMmzNpkRHaC95pjDJG NlHfZeNcIyxyW3qJ7eyR2zeXbqrcK9ERXjtu4bFvYAFp03A2X6CL+P3V6WG+f3IevxuD7VruzVpSJ 6g23s/Ew==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xEKsi-00000001kgw-07Ld; Wed, 07 Oct 2026 06:12:00 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xEKsg-00000001kgn-3KVF for kexec@lists.infradead.org; Wed, 07 Oct 2026 06:11:58 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id E082D601FB; Wed, 7 Oct 2026 06:11:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 788F71F0089B; Wed, 7 Oct 2026 06:11:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791353517; bh=SHTNYtREyl/jHXCf21L5IlTPz5bWxE9lwwBn75z0B7g=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GUXRZ7/pbe/AJpkN5e5FcdLKuJgDihokRM9FwbQxVdtvp+2LRSkZRdVJpTE58W4V6 NadEbJJreUG5ZHlSm5lZ/kScR9TQREkuTlYMfmadYLCnnhcsFnoxqr2OiLnEUNZWuq ezVr4PgORcyU4YJMkI9wQr6DJOzeoucauYENm7ogq5W1+ZswY3InNw/cE9J6Qp5m7D cvQCMK5tlmnYwkiHKEmF5ux/U5Wfqstw1sIxE2ErO9W6TbmevR9YrLXjkXZrkcTvuD NW0AbPYQSCmA2pBAFsyhQ7q7ZYL7z/j4tXZa8uou3/iBwv4XtuDPfDM2G1wFOlRTFC ONz6uDRN7u2yA== Date: Wed, 7 Oct 2026 08:11:50 +0200 From: Mike Rapoport To: Chris Bainbridge 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-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On Tue, Oct 06, 2026 at 07:02:22PM +0100, Chris Bainbridge wrote: > 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'd even say that setting CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=n and even CONFIG_KEXEC_HANDOVER=n is a reasonable choice for a distro kernel. We don't have CONFIG_EXPERIMENTAL anymore, otherwise kho and luo would be gated by it. > 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. Thanks for the clarification. This is a bug, but since it happens for a combination of an opt-in option (kho) and a hack (memmap=) I consider it low priority. -- Sincerely yours, Mike.