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 0568B29D29A; Mon, 24 Nov 2025 05:08:11 +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=1763960893; cv=none; b=PNIN7NN0a7aQZ/HCLUdhnrw6h0FvCxJACoRe2+d+U+t8RhZ82DoY872gYwUUkBHuUm9vnk8CNUY8ILjEMCsfSLFPNyWsOLUbstzJuzuFq6lpcwH41egxmY9Ob4Poq12pQEYlCEZzYDcmnrE3acfhICNQdmPpsWeVHOVDVp4hTR8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763960893; c=relaxed/simple; bh=hieoIPxIhRSooVrU3/2wVozJyRs1qMXLmzpW8xV1wzY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Rpr3vdwRU1szvrOanwMZ4JycVih+/gN0PpI7ePJFcaM915mFjtqBc5W5VhCXwa2rCy/kFtl+4qorO567NdY9uQZ3bXaupFyz306N2/LRf+djnve+Z5iysTxV1GoK6DZwjliQfO/Mbw33oXcZWhDTRGb16dvg8FGEj/zl0BfsbQo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PGWFz4wk; 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="PGWFz4wk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 463A1C4CEF1; Mon, 24 Nov 2025 05:07:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763960891; bh=hieoIPxIhRSooVrU3/2wVozJyRs1qMXLmzpW8xV1wzY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PGWFz4wkyghWCM5P7ckMfeF1ztZvSWtS2QEwkzMCzyzCVgtFKGEkLgJqy/viT440v yaLEfYvDaQKnLSy6uR+9I+i+ZINn7SDTB+/qX8KrflY1cjgOHRmknnXDOV/u0/FvGu NNUNwqZ/xrD2U3CUlUTED32zlbalE8ApcvCTVV7fCZM+JTWXoXtS4lzsdcfGlmNLAZ /qzpXLU7vNgOw/YDtFTUPhAuvbAOle9zzBCqJRbhAWlNE1Pbz9cKm2a0gIDY1NPbmC 0aQfUTilZ7Bh0ou+L5xM7SHml4e2W0OPll/Ctzpic/zP4fsRsIy5pDrE+VWMcYh228 +PoEtTeYVePdw== Date: Mon, 24 Nov 2025 07:07:47 +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 01/22] liveupdate: luo_core: Live Update Orchestrator Message-ID: References: <20251122222351.1059049-1-pasha.tatashin@soleen.com> <20251122222351.1059049-2-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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Sun, Nov 23, 2025 at 07:15:44AM -0500, Pasha Tatashin wrote: > On Sun, Nov 23, 2025 at 6:12 AM Mike Rapoport wrote: > > > > On Sat, Nov 22, 2025 at 05:23:28PM -0500, Pasha Tatashin wrote: > > > Introduce LUO, a mechanism intended to facilitate kernel updates while > > > keeping designated devices operational across the transition (e.g., via > > > kexec). The primary use case is updating hypervisors with minimal > > > disruption to running virtual machines. For userspace side of hypervisor > > > update we have copyless migration. LUO is for updating the kernel. > > > > > > This initial patch lays the groundwork for the LUO subsystem. > > > > > > Further functionality, including the implementation of state transition > > > logic, integration with KHO, and hooks for subsystems and file > > > descriptors, will be added in subsequent patches. > > > > > > Create a character device at /dev/liveupdate. > > > > > > A new uAPI header, , will define the necessary > > > structures. The magic number for IOCTL is registered in > > > Documentation/userspace-api/ioctl/ioctl-number.rst. > > > > > > Signed-off-by: Pasha Tatashin > > > Reviewed-by: Pratyush Yadav > > > > Reviewed-by: Mike Rapoport (Microsoft) > > Thank you > > > > > with a few nits below > > > > > --- > > > > > diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig > > > index a973a54447de..90857dccb359 100644 > > > --- a/kernel/liveupdate/Kconfig > > > +++ b/kernel/liveupdate/Kconfig > > > @@ -1,4 +1,10 @@ > > > # SPDX-License-Identifier: GPL-2.0-only > > > +# > > > +# Copyright (c) 2025, Google LLC. > > > +# Pasha Tatashin > > > +# > > > +# Live Update Orchestrator > > > +# > > > > If you are adding copyrights it should have Amazon and Microsoft as well. > > I believe those from kexec_handover.c would work. > > > > @Alex? > > Sure, or I can remove all of them from Kconfig, whatever you prefer :-) Quick grepping shows that the vast majority of Kconfigs does not have copyright, let's just drop it. > > > menu "Live Update and Kexec HandOver" > > > depends on !DEFERRED_STRUCT_PAGE_INIT > > > @@ -51,4 +57,25 @@ config KEXEC_HANDOVER_ENABLE_DEFAULT > > > The default behavior can still be overridden at boot time by > > > passing 'kho=off'. > > > > > > +config LIVEUPDATE > > > + bool "Live Update Orchestrator" > > > + depends on KEXEC_HANDOVER > > > + help > > > + Enable the Live Update Orchestrator. Live Update is a mechanism, > > > + typically based on kexec, that allows the kernel to be updated > > > + while keeping selected devices operational across the transition. > > > + These devices are intended to be reclaimed by the new kernel and > > > + re-attached to their original workload without requiring a device > > > + reset. > > > + > > > + Ability to handover a device from current to the next kernel depends > > > + on specific support within device drivers and related kernel > > > + subsystems. > > > > Sorry, somehow this slipped during v6 review. > > These days LUO is less about devices and more about file descriptors :) > > Device preservation through file descriptors: memfd, iommufd, vfiofd > are all dependencies for preserving devices. > > That Kconfig description is correct and essential because the core > complexity of the LUO is the preservation of device state and I/O > across a kernel transition, which is a harder problem than just > preserving memory or files, for that we could have used a file system > instead of inventing something new with logic of can_preserve() etc. > > Device preservation requires exactly what is stated in the description > for this config: > "Ability to handover a device from current to the next kernel depends > on specific support within device drivers and related kernel > subsystems." The only subsystem that is getting upstreamed with this > series is MEMFD, it is a hard pre-requirement for iommufd > preservation; the other subsystems: VFIO, PCI, IOMMU are WIP. Ok. -- Sincerely yours, Mike.