linux-kernel - RE: [PATCH v2 0/6] IOMMUFD: Deliver IO page faults to user space

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Message-ID: <BN9PR11MB5276B1582CED568795725C198CA9A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 7 Nov 2023 08:35:10 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, Lu Baolu <baolu.lu@...ux.intel.com>
CC:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 0/6] IOMMUFD: Deliver IO page faults to user space

> From: Jason Gunthorpe <jgg@...pe.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 to
> > 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.
> 
> 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?

> 
> So I'd like to see this generalized into a channel to carry any
> events..
> 
> > 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.
> 
> 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.
> 

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?