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h=Date:From:To:Cc:Subject:In-Reply-To; b=TXo6wUbvp686W6gRZC9qm8zmd4BiXLPz+wTU2Jsq2lT4E9qOQM9JxVXC0FxlBZ5pg iVw25MMaBsEi28vn1ODnZDud0jzMfw9NP4SR4+uPXPdaQLdtGDAKm+TIOPQSuX7fjx yk/Z2M+PGaVjVwx1oP3yx6UayfL38rLK20qYZ+qf5KhiR4ygA7F/s3E+Fm1++h3vnl Z07mNXiFezn3JCqacgY51FX6uymKGoCnYQPub6wfFXnuNVTZZJIVNpB7KgHDxNkwSC unRmAtTZKUdsX9Fn3QNUMDYspPEoPO0/Xa2Weh/cf2OfnuHBRN2njlHAHVl6ZgSqzO gfcXyx/Vw6YbQ== Date: Fri, 22 May 2026 13:01:59 -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 v5 10/11] PCI: liveupdate: Do not disable bus mastering on preserved devices during kexec Message-ID: <20260522180159.GA231364@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260512184846.119396-11-dmatlack@google.com> X-Rspam-User: X-Rspamd-Queue-Id: C0AAE140010 X-Rspamd-Server: rspam03 X-Stat-Signature: 8g7stahc5zt6bso1nwhsx3bbudjkq1wa X-HE-Tag: 1779472921-73916 X-HE-Meta: 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 Ae8bq+7P 2T1G06HVJz9dp4NXvIQimGvVNfQ0BXHF39J3lq9KazizAgEw5cYF1pcA/Nezeay/zO887iFbNXaSpMiyq2YLB0NLtHAwOTqRcPl+5rRZToIp6PV8bVsABLF9P9YBlxzKIi+7wMKvAulAsBnFCN/jfLZstzHR/CY++qLhv1ld98BxiKrw71dc7ld0GgSruTCU3EczssXVxTliFMJGCaDsCmWtZNw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 12, 2026 at 06:48:45PM +0000, David Matlack wrote: > Do not disable bus mastering on outgoing preserved devices during > pci_device_shutdown() for kexec. > > Preserved devices must be allowed to perform memory transactions during > a Live Update to minimize downtime and ensure continuous operation. > Clearing the bus mastering bit would prevent these devices from issuing > any memory requests while the new kernel boots. s/minimize downtime and// Ensuring continuous operation is the critical piece here. Minimizing downtime is always good but IMO it's not actually a reason for this change. I guess what this is probably saying is that the continuous operation and Live Update are what minimizes downtime, and preserving bus mastering is a piece of that. > Because bridges upstream of preserved endpoint devices are also > automatically preserved, this change also avoids clearing bus mastering > on them. This is critical because clearing bus mastering on an upstream > bridge prevents the bridge from forwarding memory requests upstream (i.e. > it would prevent the endpoint device from accessing system RAM and doing > peer-to-peer transactions with devices not downstream of the bridge).