From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D427A3222 for ; Thu, 8 Sep 2022 13:47:25 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D788A23A; Thu, 8 Sep 2022 06:47:25 -0700 (PDT) Received: from [10.57.15.197] (unknown [10.57.15.197]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A51083F7B4; Thu, 8 Sep 2022 06:47:17 -0700 (PDT) Message-ID: Date: Thu, 8 Sep 2022 14:47:11 +0100 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [PATCH v3 0/9] iommu/amd: Add Generic IO Page Table Framework Support for v2 Page Table Content-Language: en-GB To: Joerg Roedel , Jason Gunthorpe Cc: Vasant Hegde , iommu@lists.linux.dev, suravee.suthikulpanit@amd.com References: <20220825063939.8360-1-vasant.hegde@amd.com> <77d2ea43-9752-b5f3-78ef-8cdae944eee4@amd.com> <05f9784b-15b6-2a9b-2d9e-19e1430f74e2@arm.com> From: Robin Murphy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2022-09-08 14:30, Joerg Roedel wrote: > On Thu, Sep 08, 2022 at 10:19:18AM -0300, Jason Gunthorpe wrote: >> What is the use case for having PASID nested under another level of >> translation? > > Virtualization. Basically having a device access process address spaces > inside a virtual machine. That got never put into code, but it was the > rationale behind it. For SMMUv3 it did actually get as far as a prototype[1] before the iommufd work interjected. I believe there are cloud vendors using those patches in their deployments :O Cheers, Robin. [1] https://lore.kernel.org/linux-iommu/20210423095147.27922-1-vivek.gautam@arm.com/