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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-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1344420002 X-Stat-Signature: phcqiqqep61na3ncx8kt7bc7x78cx9rk X-HE-Tag: 1789084288-145353 X-HE-Meta: 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 mU5926W4 lW3zuS2yNoINnmJkQrnoo7FTlfvHizObEK+Ba+AoiBc17c+Z3MslYVEGeX9RDQx71rc/SECctndMLg945VR1YWGUEXb8ugUJJ8eB7bmDCNHvemU5dvgstGZnyZrlwhg6sbFUvxmqafx77ITYO6IBOdbHXkACapLDsM7DD/55lJcMFC+UdQKQcXRDujD2zfUWND4S8ejYpM6Omi0FONo/SO781V/iQYciIeRK1GbR9P2qa5iu0Pp3dqH7lw673r7FISQhr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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?