From: Jason Gunthorpe <jgg@ziepe.ca>
To: Nicolin Chen <nicolinc@nvidia.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
iommu@lists.linux.dev, Alex Williamson <alex@shazbot.org>,
Alexey Kardashevskiy <aik@amd.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Jacob Pan <jacob.pan@linux.microsoft.com>,
Joerg Roedel <joro@8bytes.org>,
Jonathan Cameron <jic23@kernel.org>,
Jonathan Hunter <jonathanh@nvidia.com>,
Kevin Tian <kevin.tian@intel.com>,
Krishna Reddy <vdumpa@nvidia.com>, Lukas Wunner <lukas@wunner.de>,
Robin Murphy <robin.murphy@arm.com>,
Samuel Ortiz <sameo@rivosinc.com>,
Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
Steven Price <steven.price@arm.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Thierry Reding <thierry.reding@kernel.org>,
Vasant Hegde <vasant.hegde@amd.com>,
Will Deacon <will@kernel.org>,
Xu Yilun <yilun.xu@linux.intel.com>,
kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-pci@vger.kernel.org, linux-tegra@vger.kernel.org,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v8 13/15] iommufd/viommu: Allow vIOMMUs without a parent HWPT
Date: Thu, 5 Nov 2026 14:21:06 -0400 [thread overview]
Message-ID: <20261105182106.GD663069@ziepe.ca> (raw)
In-Reply-To: <auzAivzpzSUHjEQj@nvidia.com>
On Thu, Nov 05, 2026 at 09:44:42AM -0800, Nicolin Chen wrote:
> On Thu, Nov 05, 2026 at 10:58:06AM +0530, Aneesh Kumar K.V wrote:
> > Jason Gunthorpe <jgg@ziepe.ca> writes:
> > > On Wed, Nov 04, 2026 at 11:03:41AM -0800, Nicolin Chen wrote:
> > >> By dropping the nesting parent from VIOMMU, it just simplifies the
> > >> attachment to an S1 paging hwpt, right?
> > >
> > > Yes.
> > >
> > > The VMM must always maintain a S1 paging attachment that is the
> > > identity map of the VM on all devices, same action as when there is no
> > > viommu.
> > >
> >
> > I am currently creating an S2 paging attachment. This results in a
> > configuration with S1 disabled and S2 enabled, which is used by all
> > untrusted devices.
>
> For validation, that would work. Yet "no viommu" should would be S1
> paging, i.e. hwpt allocated without IOMMU_HWPT_ALLOC_NEST_PARENT.
It doesn't matter, consistently using a single S2 for everything is
probably better..
The VMM should try to minimize the number of hwpts involved, ideally
just one per NUMA
Jason
next prev parent reply other threads:[~2026-11-05 18:21 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-04 16:16 [PATCH v8 00/15] iommufd: TSM-backed virtual IOMMUs for confidential guests Aneesh Kumar K.V (Arm)
2026-11-04 16:16 ` [PATCH v8 01/15] PCI/TSM: Move core code into its own directory Aneesh Kumar K.V (Arm)
2026-11-04 16:23 ` sashiko-bot
2026-11-05 12:24 ` kernel test robot
2026-11-04 16:16 ` [PATCH v8 02/15] virt: coco: tsm: Remove the device from lookup before PCI teardown Aneesh Kumar K.V (Arm)
2026-11-04 16:27 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 03/15] virt: coco: tsm: Complete PCI registration before publishing the device Aneesh Kumar K.V (Arm)
2026-11-04 16:32 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 04/15] virt: coco: tsm: Require PCI operations when registering a TSM Aneesh Kumar K.V (Arm)
2026-11-04 16:36 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 05/15] iommufd/device: Associate KVM file pointer with iommufd_device Aneesh Kumar K.V (Arm)
2026-11-04 16:40 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 06/15] iommufd/device: Hold a KVM file reference for the device lifetime Aneesh Kumar K.V (Arm)
2026-11-04 16:43 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 07/15] iommufd/viommu: Keep a reference to the KVM file Aneesh Kumar K.V (Arm)
2026-11-04 16:35 ` Jacob Pan
2026-11-04 16:46 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 08/15] iommufd: Add a vDEVICE operation ioctl framework Aneesh Kumar K.V (Arm)
2026-11-04 16:54 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 09/15] PCI/TSM: Remove the legacy guest request interface Aneesh Kumar K.V (Arm)
2026-11-04 16:56 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 10/15] PCI/TSM: Add vIOMMU-bound device contexts Aneesh Kumar K.V (Arm)
2026-11-04 17:07 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 11/15] iommufd/viommu: Select vIOMMU operations before allocation Aneesh Kumar K.V (Arm)
2026-11-04 17:14 ` sashiko-bot
2026-11-05 9:10 ` kernel test robot
2026-11-05 14:49 ` kernel test robot
2026-11-04 16:16 ` [PATCH v8 12/15] iommufd/viommu: Allow PCI TSM backends to provide vIOMMU operations Aneesh Kumar K.V (Arm)
2026-11-04 17:19 ` sashiko-bot
2026-11-04 23:23 ` Jacob Pan
2026-11-05 0:49 ` Jason Gunthorpe
2026-11-05 17:16 ` Jacob Pan
2026-11-04 16:16 ` [PATCH v8 13/15] iommufd/viommu: Allow vIOMMUs without a parent HWPT Aneesh Kumar K.V (Arm)
2026-11-04 17:25 ` sashiko-bot
2026-11-04 19:03 ` Nicolin Chen
2026-11-04 19:31 ` Jason Gunthorpe
2026-11-05 5:28 ` Aneesh Kumar K.V
2026-11-05 17:44 ` Nicolin Chen
2026-11-05 18:21 ` Jason Gunthorpe [this message]
2026-11-05 18:40 ` Nicolin Chen
2026-11-05 20:07 ` Jason Gunthorpe
2026-11-04 16:16 ` [PATCH v8 14/15] PCI/TSM: Wait for device contexts before removing a DSM Aneesh Kumar K.V (Arm)
2026-11-04 17:41 ` sashiko-bot
2026-11-04 16:16 ` [PATCH v8 15/15] PCI/TSM: Wait for users during unregister Aneesh Kumar K.V (Arm)
2026-11-04 18:00 ` sashiko-bot
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