From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 049D82F616A; Wed, 7 Oct 2026 06:11:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791353518; cv=none; b=MWD5yG2CGSmpBsIw15nC8o2YwACJEVXFEjkMJj4teIGOSQWKHxci0VYBjtISf7hHa55TcctzyexZrsBpQaV6lrCykLH4CFap3Sad+U2VlDfODZa78cLDw98BFkDRpvd1lD3XjQHpjTzn5jdJOWay+Puc622Kw65awrMP9xQleFE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791353518; c=relaxed/simple; bh=RiidPASTt6jyBz3Coh9BgHlpFZQ3PdK4p4NxzKF6bVQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aZ9CCCyhNBov7pxfkjCkw2d3mrLqvI4nXS+0rCXLIH2xe99PlsxVd2NWf0KmyyohDngKbBVf4W59QpExbwgJ3tNWXG4lRDyP6EMD+x85fzS3goMfs0JYwhdRj3n2qy2NmrHH7O8ZjVRcCqUQDwGFtTiXFhip+QZrCSmEHzURkyo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GUXRZ7/p; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GUXRZ7/p" 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: 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 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.