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Fri, 27 Jan 2023 15:39:40 -0800 Date: Fri, 27 Jan 2023 15:39:38 -0800 From: Nicolin Chen To: , Robin Murphy CC: , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH 1/4] iommu: Add a broken_unmanaged_domain flag in iommu_ops Message-ID: References: <0875479d24a53670e17db8a11945664a6bb4a25b.1674849118.git.nicolinc@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN8NAM11FT085:EE_|DM4PR12MB5937:EE_ X-MS-Office365-Filtering-Correlation-Id: 5bc398bf-c11a-49f5-09e4-08db00bfc7a0 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:216.228.118.232;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge1.nvidia.com;CAT:NONE;SFS:(13230025)(4636009)(396003)(346002)(39860400002)(376002)(136003)(451199018)(40470700004)(36840700001)(46966006)(70586007)(82310400005)(26005)(186003)(86362001)(9686003)(478600001)(36860700001)(40460700003)(316002)(110136005)(40480700001)(54906003)(33716001)(8676002)(4326008)(55016003)(70206006)(356005)(336012)(41300700001)(47076005)(426003)(8936002)(53546011)(83380400001)(82740400003)(5660300002)(7416002)(2906002)(7636003)(67856001);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jan 2023 23:39:48.0496 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5bc398bf-c11a-49f5-09e4-08db00bfc7a0 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.232];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT085.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB5937 Precedence: bulk List-ID: X-Mailing-List: linux-tegra@vger.kernel.org Hi Robin. On Fri, Jan 27, 2023 at 09:58:46PM +0000, Robin Murphy wrote: > External email: Use caution opening links or attachments > > > On 2023-01-27 20:04, Nicolin Chen wrote: > > Both IOMMU_DOMAIN_UNMANAGED and IOMMU_DOMAIN_DMA require the support > > of __IOMMU_DOMAIN_PAGING capability, i.e. iommu_map/unmap. However, > > some older iommu drivers do not fully support that, and these drivers > > also do not advertise support for dma-iommu.c via IOMMU_DOMAIN_DMA, > > or use arm_iommu_create_mapping(), so largely their implementations > > of IOMMU_DOMAIN_UNMANAGED are untested. This means that a user like > > vfio/iommufd does not likely work with them. > > > > Several of them have obvious problems: > > * fsl_pamu_domain.c > > Without map/unmap ops in the default_domain_ops, it isn't an > > unmanaged domain at all. > > * mtk_iommu_v1.c > > With a fixed 4M "pagetable", it can only map exactly 4G of > > memory, but doesn't set the aperture. > > The aperture is easily fixed (one could argue that what's broken there > are the ARM DMA ops for assuming every IOMMU has a 32-bit IOVA space and > not checking). > > > * tegra-gart.c > > Its notion of attach/detach and groups has to be a complete lie to > > get around all the other API expectations. > > That's true, and the domain is tiny and not isolated from the rest of > the address space outside the aperture, but the one thing it does do is > support iommu_map/unmap just fine, which is what this flag is documented > as saying it doesn't. > > > Some others might work but have never been tested with vfio/iommufd: > > * msm_iommu.c > > * omap-iommu.c > > * tegra-smmu.c > > And yet they all have other in-tree users (GPUs on MSM and Tegra, > remoteproc on OMAP) that allocate unmanaged domains and use > iommu_map/unmap just fine, so they're clearly not broken either. > > On the flipside, you're also missing cases like apple-dart, which can > have broken unmanaged domains by any definition, but only under certain > conditions (at least it "fails safe" and they will refuse attempts to > attach anything). I'd also question sprd-iommu, which hardly has a > generally-useful domain size, and has only just recently gained the > ability to unmap anything successfully. TBH none of the SoC IOMMUs are > likely to ever be of interest to VFIO or IOMMUFD, since the only things > they could assign to userspace are the individual devices - usually > graphics and media engines - that they're coupled to, whose useful > functionality tends to depend on clocks, phys, and random other > low-level stuff that would be somewhere between impractical and > downright unsafe to attempt to somehow expose as well. Thanks for all the inputs. > > Thus, mark all these drivers as having "broken" UNAMANGED domains and > > add a new device_iommu_unmanaged_supported() API for vfio/iommufd and > > dma-iommu to refuse to work with these drivers. > > > > Co-developed-by: Jason Gunthorpe > > Signed-off-by: Jason Gunthorpe > > Signed-off-by: Nicolin Chen > > [...] > > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > > index 46e1347bfa22..919a5dbad75b 100644 > > --- a/include/linux/iommu.h > > +++ b/include/linux/iommu.h > > @@ -245,6 +245,10 @@ struct iommu_iotlb_gather { > > * pasid, so that any DMA transactions with this pasid > > * will be blocked by the hardware. > > * @pgsize_bitmap: bitmap of all possible supported page sizes > > + * @broken_unmanaged_domain: IOMMU_DOMAIN_UNMANAGED is not fully functional; the > > + * driver does not really support iommu_map/unmap, but > > + * uses UNMANAGED domains for the IOMMU API, called by > > + * other SOC drivers. > > "uses UNMANAGED domains for the IOMMU API" is literally the definition > of unmanaged domains :/ > > Some "other SOC drivers" use more of the IOMMU API than VFIO does :/ > > Please just add IOMMU_CAP_IOMMUFD to represent whatever the nebulous > requirements of IOMMUFD actually are (frankly it's no less informative > than calling domains "broken"), handle that in the drivers you care > about and have tested, and use device_iommu_capable(). What you're > describing in this series is a capability, and we have a perfectly good > API for drivers to express those already. Plus, as demonstrated above, a > positive capability based on empirical testing will be infinitely more > robust than a negative one based on guessing. OK. I can change to IOMMU_CAP_IOMMUFD, and add to the drivers that are tested. And an IOMMU driver that wants to use IOMMUFD can add such a CAP later whenever it's ready. Yet, "IOMMU_CAP_IOMMUFD" would make the VFIO change suspicious, so perhaps the next version is just one CAP patch + one IOMMUFD patch. @Jason, any concern? Thank you Nicolin