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De Francesco" , Jakub Kicinski , "David S. Miller" , Eric Dumazet , Netdev , Maciej Fijalkowski , Jesper Dangaard Brouer , Daniel Borkmann , intel-wired-lan , Alexander Duyck , John Fastabend , Jesse Brandeburg , Alexei Starovoitov , bpf , Paolo Abeni , Ira Weiny , LKML , Tony Nguyen References: <20220629085836.18042-1-fmdefrancesco@gmail.com> <2254584.ElGaqSPkdT@opensuse> <2834855.e9J7NaK4W3@opensuse> From: Anirudh Venkataramanan In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR06CA0055.namprd06.prod.outlook.com (2603:10b6:a03:14b::32) To MW3PR11MB4764.namprd11.prod.outlook.com (2603:10b6:303:5a::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW3PR11MB4764:EE_|DS0PR11MB7285:EE_ X-MS-Office365-Filtering-Correlation-Id: 68fcc9d9-68b5-4d9e-5cd5-08da9ceb1d6b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:MW3PR11MB4764.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(376002)(366004)(346002)(136003)(39860400002)(396003)(451199015)(4326008)(66556008)(44832011)(36756003)(66476007)(31686004)(7416002)(2906002)(8936002)(5660300002)(6486002)(82960400001)(8676002)(26005)(66946007)(478600001)(966005)(53546011)(6916009)(41300700001)(6512007)(6506007)(107886003)(316002)(54906003)(6666004)(38100700002)(86362001)(31696002)(2616005)(186003)(45980500001)(43740500002);DIR:OUT;SFP:1102; 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My understanding of this feedback is that >> it's safer to use kmap_local_page() instead of page_address(), because >> you don't always know how the underlying page was allocated. >> >> This approach (of using kmap_local_page() instead of page_address()) >> makes sense to me. Any reason not to go this way? >> >> [1] >> >> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-1-anirudh.venkataramanan@intel.com/ >> >> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-2-anirudh.venkataramanan@intel.com/ >> >> [2] >> https://lore.kernel.org/lkml/5d667258-b58b-3d28-3609-e7914c99b31b@intel.com/ >> >> Ani > > For the two patches you referenced the driver is the one allocating > the pages. So in such a case the page_address should be acceptable. > Specifically we are falling into alloc_page(GFP_ATOMIC) which should > fall into the first case that Dave Hansen called out. Right. However, I did run into a case in the chelsio inline crypto driver where it seems like the pages are allocated outside the driver. In such cases, kmap_local_page() would be the right approach, as the driver can't make assumptions on how the page was allocated. ... and this makes me wonder why not just use kmap_local_page() even in cases where the page allocation was done in the driver. IMO, this is simpler because a) you don't have to care how a page was allocated. kmap_local_page() will create a temporary mapping if required, if not it just becomes a wrapper to page_address(). b) should a future patch change the allocation to be from highmem, you don't have to change a bunch of page_address() calls to be kmap_local_page(). Is using page_address() directly beneficial in some way? 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a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1663886302; x=1695422302; h=message-id:date:subject:to:cc:references:from: in-reply-to:content-transfer-encoding:mime-version; bh=FrRnIzigZsdP3WieJioeHsLQGwqQcypVWSPfJY45RDM=; b=bZcfSkak5KJUzruL1hV4rBnjHs4hTv9/Mzw0r7wLhkstoMRwlUysWiIE vv9Jxuno3z+QVdA9eim2GgcUBPpFwyX2eKc8jHf5UD4xn+KNA3Cpk2tGK wF2D4gaHBu23A/fsVR7zQWZB3O755Tt6RKDlUgl+PYYadt1inahdzJOEk cBiDZTGkvZD0bunHW7gnRBmxVFCnI5oqAmLrAT1mgoLttMYDRpNGDr8lX rnMajsDTTM6rrM+oCefAmzKOjBabVfGeyUcmESwhonlzBiW00MjaCZoOC uFG4M7nmYW80vmMMnRgLxiHSq/CLx6il7qhFKmyWKczO5YRYXoD0i2Low Q==; X-Mailman-Original-Authentication-Results: smtp1.osuosl.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=bZcfSkak X-Mailman-Original-Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Subject: Re: [Intel-wired-lan] [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest_frame() X-BeenThere: intel-wired-lan@osuosl.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Wired Ethernet Linux Kernel Driver Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jesper Dangaard Brouer , Daniel Borkmann , Netdev , Alexander Duyck , John Fastabend , Alexei Starovoitov , Ira Weiny , Eric Dumazet , intel-wired-lan , Jakub Kicinski , bpf , Paolo Abeni , "Fabio M. De Francesco" , "David S. Miller" , LKML Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: intel-wired-lan-bounces@osuosl.org Sender: "Intel-wired-lan" On 9/22/2022 1:58 PM, Alexander Duyck wrote: > On Thu, Sep 22, 2022 at 1:07 PM Anirudh Venkataramanan > wrote: >> >> >> Following Fabio's patches, I made similar changes for e1000/e1000e and >> submitted them to IWL [1]. >> >> Yesterday, Ira Weiny pointed me to some feedback from Dave Hansen on the >> use of page_address() [2]. My understanding of this feedback is that >> it's safer to use kmap_local_page() instead of page_address(), because >> you don't always know how the underlying page was allocated. >> >> This approach (of using kmap_local_page() instead of page_address()) >> makes sense to me. Any reason not to go this way? >> >> [1] >> >> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-1-anirudh.venkataramanan@intel.com/ >> >> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-2-anirudh.venkataramanan@intel.com/ >> >> [2] >> https://lore.kernel.org/lkml/5d667258-b58b-3d28-3609-e7914c99b31b@intel.com/ >> >> Ani > > For the two patches you referenced the driver is the one allocating > the pages. So in such a case the page_address should be acceptable. > Specifically we are falling into alloc_page(GFP_ATOMIC) which should > fall into the first case that Dave Hansen called out. Right. However, I did run into a case in the chelsio inline crypto driver where it seems like the pages are allocated outside the driver. In such cases, kmap_local_page() would be the right approach, as the driver can't make assumptions on how the page was allocated. ... and this makes me wonder why not just use kmap_local_page() even in cases where the page allocation was done in the driver. IMO, this is simpler because a) you don't have to care how a page was allocated. kmap_local_page() will create a temporary mapping if required, if not it just becomes a wrapper to page_address(). b) should a future patch change the allocation to be from highmem, you don't have to change a bunch of page_address() calls to be kmap_local_page(). Is using page_address() directly beneficial in some way? Ani _______________________________________________ Intel-wired-lan mailing list Intel-wired-lan@osuosl.org https://lists.osuosl.org/mailman/listinfo/intel-wired-lan