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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?g0x4PdhNbxK466WSy6lEzpWGsD2enYR2XW9lGQ8ar8MOhYKDLYZWX/KpMpg6?= =?us-ascii?Q?YhP5Zcd/QYtMpDga9y6urR6RDd0FkCw5RirGpdJb5L1wAvkFdq2bbraNl9YJ?= =?us-ascii?Q?ojLR0ecig4whs5DEcSCqMINxk6JSagGDScWkzQOYav4la3FysMwPxvxXnxBe?= =?us-ascii?Q?ZDMQaV6CMEhAvZozVy36GsO5wROQmRpKBbm72kMJzhxt+Ge0sinChgqulmh0?= =?us-ascii?Q?r/bd11wAFiXNbZ6yn7Vgt5mixcj1ulDbenwXZeYcR4+7O+UlPc1ZalCWKXa4?= =?us-ascii?Q?PrB0Ag4snYCc9/SPxgPHe+cIdk3oXnvhxdQvZ1XoGHkpyywa4eHHVsKfAzVx?= =?us-ascii?Q?tclTLDUYvHcs+bu0n9sA3t/KO0D6Ldqv8+AoduWRu8iTNSPfjrwzKJPlraK9?= =?us-ascii?Q?62KWcwWJh4ujniBsY5rjJrntBop5VcwDfuK51kZS65WKu3dJkHl47EWtC6wl?= =?us-ascii?Q?Q4z6v2UhUkC4x6hASq/hYGJMebu3DhHzXv+9QFg5Ivy/O+7jWc13zHBPJTQi?= =?us-ascii?Q?kgmtaL/AMtHHtZqSAe2105dIULzXyaJXQpmpf7EY7M4XXEfPphgA5g9ysz1G?= =?us-ascii?Q?tPNP4EVyNcJOuUMcNco+JBikgAmKPW9zPPii9Xt+NO3CSLjdglTDFY7VP7aM?= =?us-ascii?Q?L3nvBxfU0xQgLxhF7xvorjtOF+8bvhKhaOORnpE85RVudetFwd6gJCDOH2sJ?= =?us-ascii?Q?C9VYaXvZYWFy0x690efnNHBe69RXVkQaxpn5oKRWW1QuPuIGesawGz5fXTBI?= =?us-ascii?Q?NzX5VhqLejdkNJnoAkCI2985lW9qGKCsaBfvzf77KsDSliffcVgKTXL4VrBY?= =?us-ascii?Q?hIMF1Rpvwsrcdu7NPBK3TbN7oCuNBhTb3d1+Afv5VArzj/rlLiORYp0j+ddd?= =?us-ascii?Q?GQWDKzuC5jFib6/Cq1ERdL8Ng2oHtwfzVpLTVJ2cv+yIfOiAxaSLkZJJFnc8?= =?us-ascii?Q?SP5/imx41+DynrqncIBv9GPUuiOiu+FDTnImgFVBQhb9BF3rUi/P0xA0A+HO?= =?us-ascii?Q?XtAQvDeJs8FzurSC+DWCVdpfKNgqVm86XIPqSEf1yvR5OvbGxgX36M/XKNc1?= =?us-ascii?Q?u37JpXY4UdkLzeb4D5goXUdcF9Oy76vHF2sZUYuyMi8bz4ZIrHPOqkJ8vKo4?= =?us-ascii?Q?WqiuYKzfh5NcjpbgQ57MewERpfp/OkkvQax7Qrs0T9ps3OplY0Tc5Eql4KqO?= =?us-ascii?Q?O2WBCZXHSSf6SOa0u3KVNJemYIjjwkpHI20awsNENONVxw/dyVOJt4zIuGFW?= =?us-ascii?Q?YXkWfJgCC6F3GHjktx+PVZLrx/LsZhbCDyZxc2vt4bhRuCWy9a6NZ+bk1CUt?= =?us-ascii?Q?j6gpB9k4oKGhIIa7oTqlQtmN6gDhapfl9ddR7bZofP3G/Q=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2f47e43e-5c0c-4f89-c38e-08d98763d179 X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Oct 2021 18:21:43.7208 (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: OF8LpIkgKVgrylBDvOP5PItQRBVePhmHkxgbQST5ysYOjYCpVbhnpWNxOTKzrANd X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5064 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 04, 2021 at 09:40:03AM -0700, Jacob Pan wrote: > Hi Barry, > > On Sat, 2 Oct 2021 01:45:59 +1300, Barry Song <21cnbao@gmail.com> wrote: > > > > > > > > I assume KVA mode can avoid this iotlb flush as the device is using > > > > the page table of the kernel and sharing the whole kernel space. But > > > > will users be glad to accept this mode? > > > > > > You can avoid the lock be identity mapping the physical address space > > > of the kernel and maping map/unmap a NOP. > > > > > > KVA is just a different way to achive this identity map with slightly > > > different security properties than the normal way, but it doesn't > > > reach to the same security level as proper map/unmap. > > > > > > I'm not sure anyone who cares about DMA security would see value in > > > the slight difference between KVA and a normal identity map. > > > > yes. This is an important question. if users want a high security level, > > kva might not their choice; if users don't want the security, they are > > using iommu passthrough. So when will users choose KVA? > Right, KVAs sit in the middle in terms of performance and security. > Performance is better than IOVA due to IOTLB flush as you mentioned. Also > not too far behind of pass-through. The IOTLB flush is not on a DMA path but on a vmap path, so it is very hard to compare the two things.. Maybe vmap can be made to do lazy IOTLB flush or something and it could be closer > Security-wise, KVA respects kernel mapping. So permissions are better > enforced than pass-through and identity mapping. Is this meaningful? Isn't the entire physical map still in the KVA and isn't it entirely RW ? 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2BCC5C433F5 for ; Mon, 4 Oct 2021 18:21:56 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BFB106138B for ; Mon, 4 Oct 2021 18:21:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org BFB106138B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lists.linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 9305E405FE; Mon, 4 Oct 2021 18:21:55 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id f5vRdzdfJYso; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Oct 04, 2021 at 09:40:03AM -0700, Jacob Pan wrote: > Hi Barry, > > On Sat, 2 Oct 2021 01:45:59 +1300, Barry Song <21cnbao@gmail.com> wrote: > > > > > > > > I assume KVA mode can avoid this iotlb flush as the device is using > > > > the page table of the kernel and sharing the whole kernel space. But > > > > will users be glad to accept this mode? > > > > > > You can avoid the lock be identity mapping the physical address space > > > of the kernel and maping map/unmap a NOP. > > > > > > KVA is just a different way to achive this identity map with slightly > > > different security properties than the normal way, but it doesn't > > > reach to the same security level as proper map/unmap. > > > > > > I'm not sure anyone who cares about DMA security would see value in > > > the slight difference between KVA and a normal identity map. > > > > yes. This is an important question. if users want a high security level, > > kva might not their choice; if users don't want the security, they are > > using iommu passthrough. So when will users choose KVA? > Right, KVAs sit in the middle in terms of performance and security. > Performance is better than IOVA due to IOTLB flush as you mentioned. Also > not too far behind of pass-through. The IOTLB flush is not on a DMA path but on a vmap path, so it is very hard to compare the two things.. Maybe vmap can be made to do lazy IOTLB flush or something and it could be closer > Security-wise, KVA respects kernel mapping. So permissions are better > enforced than pass-through and identity mapping. Is this meaningful? Isn't the entire physical map still in the KVA and isn't it entirely RW ? Jason _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu