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 881A1C79FBB for ; Thu, 10 Sep 2026 23:51:30 +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: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:References: List-Owner; bh=EchVdgHD/jaEOcGNwu9K1D/RE/PHTaZPan+sGsBz7Hg=; b=laJIqFAprCxcOp +oEj3paBbtXTygTqJktFXnobiqTOjyYtV8slFEKjDcHewJSO43mLA7u2QRXDukq05VVVj7CiZLpDa Np1j+vHy91v8eWQ54u6pPCfKv4H19rEBZv4gfv02n5SFxw0N5IGna3fgB3VLdbl/v3dSMZwyV0DSA yCssLCyWiDXTA9kfOvW1ZJN/nTim+nP4/US/PilDAj4GNNYKFJQU6FjncnqwrNJqufapRaPGeqGdr +mRe+G2G+g1CDMDZRl8EqsPzwAT6j4OZ9x3/Fadw35N6i5xfOTh2Blwn2HVoyMvLQUAnRroDrQxjp 3AxN0mrZUbeYeQfa5HxA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4oYD-0000000FaOC-1dC9; Thu, 10 Sep 2026 23:51:29 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4oYC-0000000FaNv-1lj0 for kexec@lists.infradead.org; Thu, 10 Sep 2026 23:51:28 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 14449439AC; Thu, 10 Sep 2026 23:51:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2AF91F000FF; Thu, 10 Sep 2026 23:51:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789084288; bh=EchVdgHD/jaEOcGNwu9K1D/RE/PHTaZPan+sGsBz7Hg=; h=Date:From:To:Cc:Subject:In-Reply-To; b=eVJaDbr7TDZmKSMVzTSzTnbr6LHPdVB4T8TxUGUgkzVL2dnOJj+wLioEQMQFNT3ah EDa8rpCFBgV+rnysoPzaOpgFMxYYbo6Pqs9IDGAnRjH1SCRWeQAno8HW7ro0Srunsp TwjzW2QzUsiPSGwBN81N923kRd+vNzY/mtS3h5Mgqmm0nw5zmAtkqRGBLWuvO0dk/y T7sC6NnhLKcVOV0B9w3Q2t3F20Bkgj7A8yWD4vKMGvehrAyuHIexfk0nS8hyD53iNM M3Au8yPby2Gvs2mOCaOtk75szaMwkTrZFJK3RlCxg0htPYfabgJWieRiyt71eR9ILS HiP7AziEsSSfg== Date: Thu, 10 Sep 2026 18:51:26 -0500 From: Bjorn Helgaas To: David Matlack Cc: kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, Adithya Jayachandran , Alexander Graf , Alex Williamson , Bjorn Helgaas , Chris Li , David Rientjes , Jacob Pan , Jason Gunthorpe , Jonathan Corbet , Josh Hilke , Leon Romanovsky , Lukas Wunner , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pranjal Shrivastava , Pratyush Yadav , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Vipin Sharma , William Tu , Yi Liu Subject: Re: [PATCH v8 06/12] PCI: liveupdate: Auto-preserve upstream bridges across Live Update Message-ID: <20260910235126.GA367952@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260728221007.2098560-7-dmatlack@google.com> 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, Jul 28, 2026 at 10:10:00PM +0000, David Matlack wrote: > When a PCI device is preserved across a Live Update, all of its upstream > bridges up to the root port must also be preserved. This enables the PCI > core and any drivers bound to the bridges to manage bridges correctly > across a Live Update. > > Notably, this will be used in subsequent commits to ensure that > preserved devices can continue performing memory transactions without a > disruption or change in routing. > > To preserve bridges, the PCI core tracks the number of downstream > devices preserved under each bridge using a reference count in struct > pci_dev_ser. This allows a bridge to remain preserved until all its > downstream preserved devices are unpreserved or finish their > participation in the Live Update. This seems to hint that we're going to allow bridge reconfiguration in some cases, e.g., for hot-adds. The simplest case is "leave config of all bridges the same", and I thought that was what the previous patch commit log said. What's the benefit added by this patch?