Re: [PATCH RFC PREVIEW 0/6] iommu: enable user space iopfs in non-nested and non-svm cases

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Aug 26, 2024 at 01:40:26PM +0200, Klaus Jensen wrote:
> This is a Request for Comment series that will hopefully generate
> initial feedback on the use of the iommufd_hwpt_replace_device to
> execute non-nested and non-svm user space IOPFs. Our main motivation is
> to enable user-space driver driven device verification with default
> pasid and without nesting nor SVM.
> 
> What?
>   * Enable IO page fault handling in user space in a non-nested, non-svm
>     and non-virtualised use case.
>   * Removing the relation between IOPF and INTEL_IOMMU_SVM by allowing
>     the user to (de)select the IOPF code through Kconfig.
>   * Create a new file under iommu/intel (prq.c) that contains all the
>     page request queue related logic and is not under intel/svm.c.
>   * Add the IOMMU_HWPT_FAULT_ID_VALID to the valid flags used to create
>     IOMMU_HWPT_ALLOC allocations.
>   * Create a default (zero) pasid handle and insert it to the pasid
>     array within the dev->iommu_group when replacing the old HWPT with
>     an iopf enabled HWPT.
> 
> Why?
>   The PCI ATS Extended Capability allows peripheral devices to
>   participate in the caching of translations when operating under an
>   IOMMU. Further, the ATS Page Request Interface (PRI) Extension allows
>   devices to handle missing mappings. Currently, PRI is mainly used in
>   the context of Shared Virtual Addressing, requiring support for the
>   Process Address Space Identifier (PASID) capability, but other use
>   cases such as enabling user-space driver driven device verification
>   and reducing memory pinning exists. This patchest sets out to enable
>   these use cases.

I definitely expect PRI to work outside PASID and SVA cases, so this
is going in a good direction

>   Supplementary repositories supporting this patchset:
>     1. A user space library libvfn [1] which is used for testing and
>        verification (see examples/iopf.c), and

That's pretty neat, I've been wanting to see some kind of IOMMU test
suite based around a capable widely available device. This is the
closest I've seen..

Jason