From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CB0724A3E; Sun, 23 Nov 2025 11:27:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763897273; cv=none; b=mQvRsBJxghmm5ZFo/kp/feAerDiqpw4+Kt0jbKBAZ77FrkX+Sna6OHU8xnI90xdosazlTHkUu3CdM4dlTFKymRdMqey8h2x/o2bqj7mYP73GLa5CebxCrprwbTnzDOo/2dsAM4iLlD3jABbtAtkWWL++cV2jzKj+PUMJZR3hd1o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763897273; c=relaxed/simple; bh=RJWIVQsLtFDoyAvibb81H4g0e9OZxXyGb1K+TZ25eXY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=McNZmt+mUlj+GZLnd0ZwwiFdsgW1ZzWpARz4adhHQVitCgWtgZ2mNi2O4FIh4sHxuDZMlMk9on9xIdDMyOttpATQjshANXr+cgi2m6fT3CeSKngtn4QjG6HCLBnyr/kW2bcs0g72ZVLkp+TmUQchtTE3K3uM2YpMDEBXqes9wcA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jZfhzArV; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jZfhzArV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81E13C113D0; Sun, 23 Nov 2025 11:27:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763897273; bh=RJWIVQsLtFDoyAvibb81H4g0e9OZxXyGb1K+TZ25eXY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jZfhzArVLsHjBLAt4XfmVUPyRn0SeJFdACvw4DklTg6IwoSkyvWAxaTwaUzX5RovI 8Ro3Rybx/tN/ig+tzrDpbhvhKWQs91mVGH3w1TMmmJM8GuFTmx7TRTsvjR4gzEP3Wa FEDrs+JFT5Z5zVtyXtQ9gR2ileWiTGLSzoPSJMN6/ENL3Wo6C2Z8ZfNVbGgWThRiPv ACYYicPxsYIB9jNmgOh5MjWjbHIHPmz5Wa1wJtO4VeYlWidpQ4Gh4m9ob80amNlYY7 CSHDsdJdaPIjLqr94IsAAz4Wy+fSieoJq2C2kUgoLQEWd5QCFEGKZRJZFGH7YDR9ja 8Q5Wl2RANnndg== Date: Sun, 23 Nov 2025 13:27:31 +0200 From: Mike Rapoport To: Pasha Tatashin Cc: pratyush@kernel.org, jasonmiu@google.com, graf@amazon.com, dmatlack@google.com, rientjes@google.com, corbet@lwn.net, rdunlap@infradead.org, ilpo.jarvinen@linux.intel.com, kanie@linux.alibaba.com, ojeda@kernel.org, aliceryhl@google.com, masahiroy@kernel.org, akpm@linux-foundation.org, tj@kernel.org, yoann.congal@smile.fr, mmaurer@google.com, roman.gushchin@linux.dev, chenridong@huawei.com, axboe@kernel.dk, mark.rutland@arm.com, jannh@google.com, vincent.guittot@linaro.org, hannes@cmpxchg.org, dan.j.williams@intel.com, david@redhat.com, joel.granados@kernel.org, rostedt@goodmis.org, anna.schumaker@oracle.com, song@kernel.org, linux@weissschuh.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, gregkh@linuxfoundation.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, rafael@kernel.org, dakr@kernel.org, bartosz.golaszewski@linaro.org, cw00.choi@samsung.com, myungjoo.ham@samsung.com, yesanishhere@gmail.com, Jonathan.Cameron@huawei.com, quic_zijuhu@quicinc.com, aleksander.lobakin@intel.com, ira.weiny@intel.com, andriy.shevchenko@linux.intel.com, leon@kernel.org, lukas@wunner.de, bhelgaas@google.com, wagi@kernel.org, djeffery@redhat.com, stuart.w.hayes@gmail.com, ptyadav@amazon.de, lennart@poettering.net, brauner@kernel.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, saeedm@nvidia.com, ajayachandra@nvidia.com, jgg@nvidia.com, parav@nvidia.com, leonro@nvidia.com, witu@nvidia.com, hughd@google.com, skhawaja@google.com, chrisl@kernel.org Subject: Re: [PATCH v7 02/22] liveupdate: luo_core: integrate with KHO Message-ID: References: <20251122222351.1059049-1-pasha.tatashin@soleen.com> <20251122222351.1059049-3-pasha.tatashin@soleen.com> Precedence: bulk X-Mailing-List: linux-api@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: <20251122222351.1059049-3-pasha.tatashin@soleen.com> On Sat, Nov 22, 2025 at 05:23:29PM -0500, Pasha Tatashin wrote: > Integrate the LUO with the KHO framework to enable passing LUO state > across a kexec reboot. > > This patch implements the lifecycle integration with KHO: > > 1. Incoming State: During early boot (`early_initcall`), LUO checks if > KHO is active. If so, it retrieves the "LUO" subtree, verifies the > "luo-v1" compatibility string, and reads the `liveupdate-number` to > track the update count. > > 2. Outgoing State: During late initialization (`late_initcall`), LUO > allocates a new FDT for the next kernel, populates it with the basic > header (compatible string and incremented update number), and > registers it with KHO (`kho_add_subtree`). > > 3. Finalization: The `liveupdate_reboot()` notifier is updated to invoke > `kho_finalize()`. This ensures that all memory segments marked for > preservation are properly serialized before the kexec jump. > > LUO now depends on `CONFIG_KEXEC_HANDOVER`. > > Signed-off-by: Pasha Tatashin > --- > include/linux/kho/abi/luo.h | 54 +++++++++++ > kernel/liveupdate/luo_core.c | 154 ++++++++++++++++++++++++++++++- > kernel/liveupdate/luo_internal.h | 22 +++++ > 3 files changed, 229 insertions(+), 1 deletion(-) > create mode 100644 include/linux/kho/abi/luo.h > create mode 100644 kernel/liveupdate/luo_internal.h > > diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h > new file mode 100644 > index 000000000000..8523b3ff82d1 > --- /dev/null > +++ b/include/linux/kho/abi/luo.h > @@ -0,0 +1,54 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +/* > + * Copyright (c) 2025, Google LLC. > + * Pasha Tatashin > + */ > + > +/** > + * DOC: Live Update Orchestrator ABI > + * > + * This header defines the stable Application Binary Interface used by the > + * Live Update Orchestrator to pass state from a pre-update kernel to a > + * post-update kernel. The ABI is built upon the Kexec HandOver framework > + * and uses a Flattened Device Tree to describe the preserved data. > + * > + * This interface is a contract. Any modification to the FDT structure, node > + * properties, compatible strings, or the layout of the `__packed` serialization > + * structures defined here constitutes a breaking change. Such changes require > + * incrementing the version number in the relevant `_COMPATIBLE` string to > + * prevent a new kernel from misinterpreting data from an old kernel. >From v6 thread: > > I'd add a sentence that stresses that ABI changes are possible as long they > > include changes to the FDT version. > > This is indeed implied by the last paragraph, but I think it's worth > > spelling it explicitly. > > > > Another thing that I think this should mention is that compatibility is > > only guaranteed for the kernels that use the same ABI version. > > Sure, I will add both. Looks like it fell between the cracks :/ > +static int __init liveupdate_early_init(void) > +{ > + int err; > + > + err = luo_early_startup(); > + if (err) { > + luo_global.enabled = false; > + luo_restore_fail("The incoming tree failed to initialize properly [%pe], disabling live update\n", > + ERR_PTR(err)); What's wrong with a plain panic()? > + } > + > + return err; > +} > +early_initcall(liveupdate_early_init); > + ... > int liveupdate_reboot(void) > { > - return 0; > + int err; > + > + if (!liveupdate_enabled()) > + return 0; > + > + err = kho_finalize(); > + if (err) { > + pr_err("kho_finalize failed %d\n", err); Nit: why not %pe? > + /* > + * kho_finalize() may return libfdt errors, to aboid passing to > + * userspace unknown errors, change this to EAGAIN. > + */ > + err = -EAGAIN; > + } > + > + return err; > } > > /** > diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h > new file mode 100644 > index 000000000000..8612687b2000 > --- /dev/null > +++ b/kernel/liveupdate/luo_internal.h > @@ -0,0 +1,22 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +/* > + * Copyright (c) 2025, Google LLC. > + * Pasha Tatashin > + */ > + > +#ifndef _LINUX_LUO_INTERNAL_H > +#define _LINUX_LUO_INTERNAL_H > + > +#include > + > +/* > + * Handles a deserialization failure: devices and memory is in unpredictable > + * state. > + * > + * Continuing the boot process after a failure is dangerous because it could > + * lead to leaks of private data. > + */ > +#define luo_restore_fail(__fmt, ...) panic(__fmt, ##__VA_ARGS__) Let's add this when we have more than a single callsite. Just use panic() in liveupdate_early_init() and add the comment there. > + > +#endif /* _LINUX_LUO_INTERNAL_H */ > -- > 2.52.0.rc2.455.g230fcf2819-goog > -- Sincerely yours, Mike.