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 C2612CD5BB4 for ; Fri, 22 May 2026 18:02:04 +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=3pwqqJmK0UZHpTQbgMPdFytZpYtz+77BknUANKGAa1k=; b=iGLgi2ZI6AXqSw DXRGsMNGpuWEq6HftwnBMBLnX93aIbbwKnbvBfmU6gfAiC/p4wSNhVOsubocwZhrBKU3qITR4t7Is rMNmade5GTzZ8YQ2f8s22uL4fFuffD1L4G/+IFAnzRwkdktyajwzxRsskJAo2Ci09p0hDKTDXgSNG ULL+2hNZ98XsMjq6evW2KJGXc3KV2edrvKHiPpdoxHi5DhUusgLd9W02Tg0owz0aITs1maC3Mucie xLpgvFXSQAwScVmiU2sKNvjddVBemnHxqYKRoW3B29NqxAKq6c5HvPasdEwJH4dHA7WkwKmkpyP7a hjhPhvbXNb/J8jXYWi0g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wQUCB-0000000BdKv-26JK; Fri, 22 May 2026 18:02:03 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wQUC9-0000000BdKQ-0s62 for kexec@lists.infradead.org; Fri, 22 May 2026 18:02:02 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with UTF8SMTP id D93A142DE8; Fri, 22 May 2026 18:02:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 91D7A1F000E9; Fri, 22 May 2026 18:02:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779472920; bh=3pwqqJmK0UZHpTQbgMPdFytZpYtz+77BknUANKGAa1k=; 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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260522_110201_266999_981BD0EF X-CRM114-Status: GOOD ( 10.71 ) 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, 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).