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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@ziepe.ca>, Lu Baolu <baolu.lu@linux.intel.com>
CC:     Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        "Robin Murphy" <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
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        "Liu, Yi L" <yi.l.liu@intel.com>,
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Subject: RE: [PATCH v2 0/6] IOMMUFD: Deliver IO page faults to user space
Thread-Topic: [PATCH v2 0/6] IOMMUFD: Deliver IO page faults to user space
Thread-Index: AQHaB7ekIyYD98ruGE6A75OvyWpVCrBnBhoAgAeTvxA=
Date:   Tue, 7 Nov 2023 08:35:10 +0000
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References: <20231026024930.382898-1-baolu.lu@linux.intel.com>
 <20231102124742.GA4634@ziepe.ca>
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> From: Jason Gunthorpe <jgg@ziepe.ca>
> Sent: Thursday, November 2, 2023 8:48 PM
>
> On Thu, Oct 26, 2023 at 10:49:24AM +0800, Lu Baolu wrote:
> > Hi folks,
> >
> > This series implements the functionality of delivering IO page faults t=
o
> > user space through the IOMMUFD framework for nested translation.
> Nested
> > translation is a hardware feature that supports two-stage translation
> > tables for IOMMU. The second-stage translation table is managed by the
> > host VMM, while the first-stage translation table is owned by user
> > space. This allows user space to control the IOMMU mappings for its
> > devices.
>=20
> Having now looked more closely at the ARM requirements it seems we
> will need generic events, not just page fault events to have a
> complete emulation.

Can you elaborate?

>=20
> So I'd like to see this generalized into a channel to carry any
> events..
>=20
> > User space indicates its capability of handling IO page faults by
> > setting the IOMMU_HWPT_ALLOC_IOPF_CAPABLE flag when allocating a
> > hardware page table (HWPT). IOMMUFD will then set up its infrastructure
> > for page fault delivery. On a successful return of HWPT allocation, the
> > user can retrieve and respond to page faults by reading and writing to
> > the file descriptor (FD) returned in out_fault_fd.
>=20
> This is the right way to approach it, and more broadly this shouldn't
> be an iommufd specific thing. Kernel drivers will also need to create
> fault capable PAGING iommu domains.
>=20

Are you suggesting a common interface used by both iommufd and
kernel drivers?

but I didn't get the last piece. If those domains are created by kernel
drivers why would they require a uAPI for userspace to specify fault
capable?