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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?Nm+gR6serET8WEH6FfubHaBjyr7D4+qBeJIWyjLRDsbMItGk4WJm6c3/rj9O?= =?us-ascii?Q?hUgOVjVfBHGWLAwM8o+1HxACdGKr2z7plBNrURaJfH3xUq/CnoQXaiWYWjsy?= =?us-ascii?Q?1cn8vEww0c4t7cNJN9fhv3JF5A9nKhnvGUDAPWdkX1xF/1AUd/QHQDA5X/Oc?= =?us-ascii?Q?LPd1mSHmHLEOvu9ng1n/e1l68bDkPNpt82ixxLCF1zmBefewk11jIBa9gBKK?= =?us-ascii?Q?vzgLOEO2DN6CDIrVe5gf2UoDYdWxn1X2Mvn47ZW5sZkAB68DaYVZ/kTIpL7/?= =?us-ascii?Q?Duy1jG5oVqhzhLoQqq5k5Bz+3C1LxHwmAFOX0e+bs2vZXHATwuzz8EgsPjBL?= =?us-ascii?Q?4bE2GUoNHQRLGK8ymV+7oTX41YZ00GWNH36FYaiqs1le9PeU32OHZroYpfJO?= =?us-ascii?Q?NHfdkqFzRU3F2wFslcTXqIJRYEk7vGIl1emrJ5qGy3qRCtQnA50RjqzxPFjB?= =?us-ascii?Q?NTKX+BHM4J/YNb4ilM/aZBdulPNzF9Vf5p4j98qbAtgmHRvxeFpMmK7tHtnv?= =?us-ascii?Q?sxfwY85LA9WHx58XOEzY1pdddVyFnvyx7mFxZsErNjb6zD9s4RJIuqNxdiK8?= =?us-ascii?Q?0xbzspyjWC9jEWrPayAc16sOoaM9qkftXDhXrjDoA2ZENBrLKxLieukg9koS?= =?us-ascii?Q?Zj4gRX9lDWVzPMwt2D5DygAl9Ta2SHIewABaDHoYxnLf0SWGwcnl/qfiGeeB?= =?us-ascii?Q?U18CkBn4NmxYfU03wPhyWdjti9FDVvKCrVpGxX9P4hJ2LXPY7f0GSTbrIlI5?= =?us-ascii?Q?lVoQpctiNVg3x7efsK6/XzlGTqb3L7hTnt4t0UerGqIx5638MVqSd0nm4Zls?= =?us-ascii?Q?S4QNHG2a2BJuUMfWV8W6lDFWe/0ZFEkljPwBi+saV5rftxAMmf5keP2uot7e?= =?us-ascii?Q?Q6VdwVQl36u7tcSw10FpbbtYk8yotBR763UBLRvgUjeIopzlIb8qGNzW0bkV?= =?us-ascii?Q?KvuDCWPVgxLFHVw8g5zxIdoZargY8CByYckIzwaeOrNwLOnQZJiJPxZRcPtb?= =?us-ascii?Q?8FDwjwa/IAsj54Pkk2g82DBZLuuN0GAeMNm355iuAI3AAr8SVypxL+u9Ih1I?= =?us-ascii?Q?MhL7Gu4O7KDRB17xSlY70RNdqaN4HXwqisIhVxGjxolhwAVRInft597ZHstk?= =?us-ascii?Q?/hnm6wgglutx/y0kf1phscmo05bhvNE+K3lOmxuzYz2K2f34rszsaLZw9x3q?= =?us-ascii?Q?vGRzv38bklxs4z+3IOuirj4cuhNHcJSN6TCN4/eJp/BxB+ArTvj7QVzHhyLq?= =?us-ascii?Q?ey3pfdnOAe1TUBHU+Gy6+wvPwvU+h5f2iuq539PEzaig0GOXT8yxljQOsVya?= =?us-ascii?Q?ei+U7O+Q+xz2FFzfbyZNk7F7LLGvdyAkAcSWAkTqy9h7/WwrSc61EQwapDVN?= =?us-ascii?Q?WK9ELnYR0uwgdHVLeS1NABDJPFuO1FC6rh/LMVVXzQVOtUXhrapVic6qcfB7?= =?us-ascii?Q?kG8d33UUhoVh20O0K45WUJCOJhUL4LeaFhzOBuxTNApmVeAQuxmqCZxvQUjf?= =?us-ascii?Q?v6+BTeiJg9qfLzh6LlsSL83sd+tr++hEqUJeQAJj7bM6Ekh3WTC3kdfF4rV/?= =?us-ascii?Q?VoFJw4o72HkGxz3dGxqPoNIXSAFE6novdZ9EmtN7?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: bc6949e5-adb7-42a7-2849-08da5632dc84 X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Jun 2022 22:42:47.6691 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: QOqirtq65UgX9LCdtBk8ZDcVwG+ghOtySzzGBzLd99rXsmwZM7AFK5fv/uoCl6O0 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB4277 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 24, 2022 at 01:12:56PM -0700, Nicolin Chen wrote: > > The kmap_local_page() arose because the code doing memcpy had to be > > updated to go from a struct page to a void * for use with memcpy and > > the kmap_local_page() is the correct API to use for that. > > > > The existing code which casts a pfn to a void * is improper. > > Yes. > > If I understand everything correctly: > > A PFN is not secure enough to promise that the memory is not IO. And > direct access via memcpy() that only handles CPU memory will crash on > S390 if the PFN is an IO PFN, as we have to use the memcpy_to/fromio() > that uses the special S390 IO access instructions. On the other hand, > a "struct page *" is always a CPU coherent thing that fits memcpy(). > > Also, casting a PFN to "void *" for memcpy() is not an proper practice, > kmap_local_page() is the correct API to call here, though S390 doesn't > use highmem, which means kmap_local_page() is a NOP. > > There's a following patch changing the vfio_pin_pages() API to return > a list of "struct page *" instead of PFNs. It will block any IO memory > from ever getting into this call path, for such a security purpose. In > this patch, add kmap_local_page() to prepare for that. Yes, basically Jason 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 DFECCCCA473 for ; Fri, 24 Jun 2022 22:42:52 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 5E43810F6C8; Fri, 24 Jun 2022 22:42:51 +0000 (UTC) Received: from NAM10-MW2-obe.outbound.protection.outlook.com (mail-mw2nam10on2043.outbound.protection.outlook.com [40.107.94.43]) by gabe.freedesktop.org (Postfix) with ESMTPS id 3FFDA10F6C4; Fri, 24 Jun 2022 22:42:50 +0000 (UTC) ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=CWH9kZFDRZNVrAy6Olb6IemiEth04hNMhUD0Be87S7Tx9Y3oqQ4D+WJsf6cLhzc4CnQXGC7FwsfKHgnDxfX40AVi+2bw5+NkBgagttMtX0nr5wuB5EOPURBDsdR6Le870NgCifCaAR4+Mdfr9q6d5/R9Im2u3m+dARrB+8Omg0SA+C+NEbf5vq6JhTps46vmtxJg/MK8C+H1ir2+P2E4/m2ja6cvZxhFQ6fajBTBLzOAhHL8BOkF6fkFSjZNiQpsOrI1qu7qMj2OSPOPcVfqyZ+/DFL0FWjwXUvbAsQD47hVXG83Jom80aNKB1PR3qb7+vucd3Ea7SAVEneBhWLDFQ== ARC-Message-Signature: i=1; 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And > direct access via memcpy() that only handles CPU memory will crash on > S390 if the PFN is an IO PFN, as we have to use the memcpy_to/fromio() > that uses the special S390 IO access instructions. On the other hand, > a "struct page *" is always a CPU coherent thing that fits memcpy(). > > Also, casting a PFN to "void *" for memcpy() is not an proper practice, > kmap_local_page() is the correct API to call here, though S390 doesn't > use highmem, which means kmap_local_page() is a NOP. > > There's a following patch changing the vfio_pin_pages() API to return > a list of "struct page *" instead of PFNs. It will block any IO memory > from ever getting into this call path, for such a security purpose. In > this patch, add kmap_local_page() to prepare for that. 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And > direct access via memcpy() that only handles CPU memory will crash on > S390 if the PFN is an IO PFN, as we have to use the memcpy_to/fromio() > that uses the special S390 IO access instructions. On the other hand, > a "struct page *" is always a CPU coherent thing that fits memcpy(). > > Also, casting a PFN to "void *" for memcpy() is not an proper practice, > kmap_local_page() is the correct API to call here, though S390 doesn't > use highmem, which means kmap_local_page() is a NOP. > > There's a following patch changing the vfio_pin_pages() API to return > a list of "struct page *" instead of PFNs. It will block any IO memory > from ever getting into this call path, for such a security purpose. In > this patch, add kmap_local_page() to prepare for that. Yes, basically Jason